Inventory management | AQA A-Level Business
For Specification 7132
AQA A-Level Business | Free Revision Notes
Estimated study time: 75 minutes
Effective inventory management means having enough inventory available to support operations and satisfy customers without holding unnecessarily large amounts. This Inventory management A-Level Business revision page covers the AQA requirements for interpreting inventory-control charts, including lead time, re-order levels, buffer inventory levels and re-order quantities. You will also analyse the factors affecting how much inventory a business chooses to hold. The topic develops lean production [Lean production] and matching supply to demand [Matching supply to demand], and provides an important foundation for decisions about suppliers and supply chains.
Learning Objectives 🎯
By the end of this revision page, you should be able to:
Explain influences on the amount of inventory a business holds.
Interpret inventory-control charts accurately.
Explain and identify lead time.
Explain and identify re-order levels.
Explain and identify buffer inventory levels.
Explain and calculate re-order quantities.
Analyse inventory-management decisions in different business contexts.
Revision Notes 📚
Inventory management A-Level Business revision overview
AQA requires students to understand influences on the amount of inventory held.
Inventory control must include:
interpreting inventory-control charts
lead time
re-order levels
buffer level of inventory
re-order quantities.
These concepts are closely connected.
Managers decide:
how much inventory should normally be held
when new inventory should be ordered
how much should be ordered
how much protection should be retained against unexpected demand or delayed deliveries.
The objective is not automatically to hold the smallest possible amount of inventory. The business needs to balance the cost of holding inventory against the risk of not having enough inventory when it is required.
What is inventory?
Inventory refers to goods or materials held by a business for future use or sale.
Depending on the business, inventory may include:
materials required for production
components
finished products awaiting sale
goods held by a retailer for customers.
A manufacturer and a retailer may therefore both manage inventory, but the type of inventory being managed differs.
AQA's 2025 examination applied Just in Time inventory management to a food retailer, illustrating that inventory management is not limited to manufacturing.
Why businesses hold inventory
A business may hold inventory so that it can:
continue operating when materials or components are required
satisfy customer demand
protect itself against delays in supply
respond to changes in demand.
However, holding inventory also uses business resources.
The central inventory-management trade-off is:
more inventory held
↓
greater protection against shortages
but:
more resources tied up in inventory and potentially greater storage or wastage costs
This is why the optimal inventory level varies between businesses.
Inventory-control charts
An inventory-control chart shows how a business's inventory level changes over time.
A typical chart has:
inventory level on the vertical axis
time on the horizontal axis.
Inventory usually falls as it is used or sold.
When a delivery arrives, the inventory level rises.
This creates the characteristic repeating pattern of an inventory-control chart.
The AQA specification explicitly requires students to be able to interpret inventory-control charts, and AQA has tested them through both calculations and graphical questions.
Illustrative inventory-control chart
The following example uses the structure of the skills AQA has assessed. The figures are illustrative.
Illustrative inventory-control pattern
Inventory falls as it is used. An order is placed when inventory reaches the re-order level, with delivery arriving after the lead time.
In this example:
maximum inventory = 6,000 units
re-order level = 2,150 units
buffer inventory level = 750 units
the order is placed on day 11
delivery arrives on day 15.
Therefore:
Lead time=15−11=4 days
The delivery increases inventory from 750 units to 6,000 units:
Re-order quantity = 6,000 − 750 = 5,250 units
These figures mirror the calculation principles AQA assessed in the June 2022 Paper 2 inventory-control questions.
Reading the downward-sloping line
The downward-sloping part of an inventory-control chart represents inventory being:
used in production
sold to customers.
A steeper downward slope means inventory is being used more quickly.
A flatter downward slope means inventory is being used more slowly.
Example
Suppose inventory falls:
by 600 units per day in Period A
by 300 units per day in Period B.
The line for Period A would be steeper.
This is important because AQA has required students to alter an inventory-control chart when demand changes.
In the 2023 Paper 1, students had to show how a reduction in demand changed the downward slope of the inventory line. The examiner report found that most students understood the delivery increase, but the new downward slope was often plotted inaccurately.
Reading the vertical increase
When new inventory arrives, the amount held increases rapidly.
On a traditional inventory-control chart, this is represented by a vertical rise.
The size of that rise represents the re-order quantity.
For example:
Inventory immediately before delivery = 1,000 units.
Inventory immediately after delivery = 5,000 units.
Therefore:
Re-order quantity = 5,000 − 1,000 = 4,000 units
AQA's 2023 Paper 1 specifically required students to draw a changed re-order quantity onto an inventory-control chart.
Lead time
What is lead time?
Lead time is the time between placing an order for inventory and receiving that inventory.
For example:
order placed on Monday
inventory arrives on Friday.
The lead time is the time between these two events.
Lead time matters because the business must continue operating during the period after ordering but before the delivery arrives.
Identifying lead time on a chart
On an inventory-control chart:
Find the point at which inventory reaches the re-order level.
This is when the new order is placed.
Find the point where the delivery arrives and inventory rises.
Calculate the difference in time.
Worked example
Re-order level reached = day 8.
Delivery arrives = day 13.
Lead time = 13−8 = 5 days = 5
Answer: 5 days
AQA's June 2022 Paper 2 required students to calculate lead time directly from an inventory-control chart. The correct answer in that assessment was four days.
Why lead time affects inventory decisions
A longer lead time means the business waits longer after ordering before replacement inventory arrives.
If inventory continues to be used during this period, the business may need to place its order earlier.
For example:
longer lead time
↓
more inventory will be used while waiting for delivery
↓
order may need to be placed at a higher inventory level
↓
re-order level may need to increase
This reduces the risk that inventory runs out before the new delivery arrives.
Shorter lead time
A shorter lead time means inventory can be replenished more quickly.
This may allow the business to:
order later
operate with a lower re-order level
potentially hold less inventory.
The possible chain is:
shorter lead time
↓
replacement inventory arrives sooner
↓
less inventory required to cover the waiting period
↓
average inventory holdings may fall
↓
inventory-related costs may fall
This helps explain why supplier performance can affect inventory-management decisions.
Re-order level
What is the re-order level?
The re-order level is the inventory level at which the business places an order for additional inventory.
For example, if a business orders more materials whenever its inventory falls to 3,000 units:
re-order level = 3,000 units
The order is not necessarily received at this point.
The business must then wait through the lead time.
Why the re-order level matters
If the re-order level is set too low:
inventory falls to a low level before order is placed
↓
inventory continues to be used during lead time
↓
inventory may run out before delivery arrives
↓
production or sales may be disrupted
If the re-order level is set unnecessarily high:
order placed relatively early
↓
replacement inventory arrives while significant existing inventory remains
↓
average inventory holdings may become higher
↓
more resources may be tied up in inventory
Managers therefore need an appropriate re-order level.
Re-order level and lead time
These two concepts are closely connected.
A business with a long lead time generally needs to order earlier than one receiving replacement inventory quickly, assuming inventory is being used at a similar rate.
Example
Business A uses 100 units per day and has a lead time of two days.
Business B uses 100 units per day and has a lead time of ten days.
Business B needs much more inventory available while waiting for delivery.
Therefore, its re-order level is likely to need to be higher.
Re-order level and rate of inventory use
The amount of inventory being used also matters.
If customer demand increases:
inventory is used more quickly
↓
downward slope on inventory chart becomes steeper
↓
inventory reaches the re-order level sooner
↓
orders need to be made more frequently if other factors remain unchanged
Managers therefore need to monitor demand rather than assuming a previous inventory pattern will continue indefinitely.
Buffer inventory level
What is buffer inventory?
Buffer inventory is the minimum level of inventory a business plans to keep as protection against uncertainty.
It provides a cushion if:
customer demand is unexpectedly high
inventory is used faster than expected
a supplier delivery is delayed.
AQA uses the terminology buffer level of inventory in the specification.
Why businesses hold buffer inventory
Suppose the business expects replacement inventory to arrive before existing inventory is completely used.
If the supplier is late, buffer inventory gives the business something to use while it waits.
The chain is:
supplier delay
↓
expected delivery does not arrive
↓
business uses buffer inventory
↓
operations may continue
↓
risk of disruption is reduced
Buffer inventory therefore protects the business from uncertainty.
A higher buffer inventory level
Increasing buffer inventory provides greater protection.
For example:
Old buffer = 500 units.
New buffer = 1,500 units.
The business now has an extra 1,000 units available if supply is delayed or demand is unexpectedly high.
Potential advantage
higher buffer inventory
↓
greater protection against unexpected demand or supplier delays
↓
lower risk of running out
↓
operations or sales can continue
↓
customer service may be protected
Potential disadvantage
higher buffer inventory
↓
more inventory normally held
↓
more money tied up in inventory
↓
potentially higher storage and wastage costs
The appropriate level therefore depends on the risk the business faces.
A lower buffer inventory level
A lower buffer level reduces the amount of inventory held for protection.
Potential advantages include:
less inventory to finance
lower storage requirements
less risk of waste where inventory is perishable.
However:
lower buffer
↓
less protection from disruption
↓
greater dependence on deliveries arriving when expected
↓
higher risk of shortages if something goes wrong
This relationship is central to Just in Time operations studied in lean production [Lean production].
Buffer inventory and supplier reliability
Supplier reliability can strongly influence the amount of buffer inventory required.
AQA's June 2022 mark scheme explicitly recognised the relationship:
businesses attempting to keep buffer stock low need reliable suppliers
a business could hold a larger buffer if it selected a less reliable supplier for other reasons.
The chain is:
supplier highly reliable
↓
lower probability of delayed delivery
↓
business may be able to operate with lower buffer inventory
↓
less cash tied up and lower holding costs
By contrast:
unreliable supplier
↓
greater risk of delayed inventory
↓
larger buffer may be needed
↓
inventory costs rise
This links directly with choosing suppliers [Choosing suppliers].
Re-order quantity
What is the re-order quantity?
The re-order quantity is the amount of inventory ordered each time a new order is placed.
On an inventory-control chart, it is represented by the increase in the inventory level when the delivery arrives.
Formula from a chart
Where the chart shows inventory immediately before and after delivery:
Re-order quantity = Inventory after delivery − Inventory before delivery
Worked example
Inventory before delivery = 800 units.
Inventory after delivery = 5,800 units.
5,800 − 800 = 5,000
Re-order quantity = 5,000 units
In AQA's 2022 Paper 2 example:
maximum inventory = 6,000 units
buffer inventory = 750 units.
Therefore:
6,000 − 750 = 5,250
Re-order quantity = 5,250 units.
Larger re-order quantities
A larger re-order quantity means more inventory arrives each time an order is received.
Potential advantages may include:
orders are required less frequently
the business may benefit from buying larger quantities where this reduces purchasing costs.
AQA's 2025 inventory-turnover mark scheme recognised bulk buying inventory as a reason inventory may be held for longer.
However, larger orders can also mean:
higher average inventory levels
more cash tied up
greater storage requirements
greater risk of waste or loss of value.
Smaller re-order quantities
Smaller quantities mean less inventory arrives on each occasion.
Potential advantages include:
lower average inventory
less storage
less cash tied up
potentially less waste.
But the business may need to order more frequently.
This is closely related to the Just in Time principles studied in lean production [Lean production].
Re-order quantity and maximum inventory
In a simple inventory-control chart:
inventory before delivery + re-order quantity = inventory after delivery
For example:
750+5,250=6,000750+5,250=6,000
Therefore:
buffer level = 750
re-order quantity = 5,250
maximum after delivery = 6,000.
Do not automatically assume the re-order quantity is the same as the re-order level. They are different concepts.
Inventory usage
Inventory-control charts can also be used to determine how quickly inventory is being used.
Suppose inventory falls from:
5,000 units
to 2,000 units
over 6 days.
Inventory used:
5,000−2,000=3,000
Daily usage:
3,000/6 = 500
Inventory usage = 500 units per day
AQA's 2022 Paper 2 required students to calculate inventory usage per day from the inventory-control chart.
Using re-order quantity to calculate usage
Suppose:
re-order quantity = 6,000 units
each delivery lasts 20 days.
Average daily usage:
6,000/20 = 300
300 units per day
The chart may therefore provide enough data for calculations even where daily usage is not written directly.
Influences on the amount of inventory held
AQA requires students to understand influences on the amount of inventory held, but does not prescribe a fixed checklist of influences. The following factors are supported by AQA assessment materials and the specified inventory concepts.
Demand
A business needs sufficient inventory to satisfy expected demand.
Higher demand may require more inventory.
For example:
sales increase
↓
inventory is used more quickly
↓
business may need more frequent or larger deliveries
↓
inventory arrangements need to change
The predictability of demand also matters.
Uncertainty of demand
If demand varies unexpectedly, holding very low inventory increases the possibility of a shortage.
A larger buffer may provide protection:
unpredictable demand
↓
actual demand may exceed forecast
↓
inventory used faster than expected
↓
buffer inventory protects against running out
However, the extra protection has a cost because more inventory is held.
Lead time
Longer lead times usually increase the need to plan further ahead.
long lead time
↓
business waits longer for replacement inventory
↓
more inventory is used during the waiting period
↓
higher re-order level or buffer may be required
Shorter lead times can make lower inventory holdings more practical.
Supplier reliability
Reliable suppliers make lower inventory levels less risky.
AQA's 2022 supplier mark scheme explicitly connected reliable suppliers with businesses that want to operate JIT systems and keep buffer inventory low.
An unreliable supplier may cause managers to retain more inventory as protection.
This factor is developed further in choosing suppliers [Choosing suppliers].
Nature of the inventory
Some inventory cannot be held successfully for long periods.
AQA's 2025 assessment of Seebus plc, a food retailer, recognised that JIT can be particularly valuable where fresh food may be wasted if inventory is not managed carefully.
Therefore:
inventory can become unusable quickly
↓
large holdings increase risk of waste
↓
business has an incentive to hold less
This factor can be especially important for retailers of fresh goods.
Storage costs and available space
Holding more inventory may require more storage.
The potential chain is:
higher inventory holdings
↓
greater storage requirement
↓
higher operating costs
↓
higher unit costs or lower profit margins
Reducing unnecessary inventory can therefore improve efficiency.
This was one of the benefits of JIT considered in lean production [Lean production].
Cash tied up in inventory
Inventory normally has to be purchased before the business can generate cash from selling it.
Therefore:
larger inventory holdings
↓
more cash committed to inventory
↓
less cash immediately available for other purposes
AQA has recognised reducing inventory as a way in which businesses may improve cash flow. This creates a useful link forward to cash flow and profit [Cash flow and profit].
Purchasing in larger quantities
A business may deliberately buy more inventory because larger purchases provide a financial advantage.
AQA's 2025 inventory-turnover mark scheme recognised bulk purchasing as a reason inventory might remain within a business for longer.
The possible advantage is:
larger purchase
↓
lower purchasing cost may be available
↓
unit input cost may fall
However:
larger purchase
↓
more inventory held
↓
storage requirements and cash tied up increase
The business therefore needs to compare the purchasing benefit with the cost of holding additional inventory.
Range of products or materials required
AQA's 2025 mark scheme also recognised that a business might need a wider range of goods or raw materials to satisfy larger customers.
A broader range may therefore increase total inventory holdings.
The significance depends on the business's products and customers.
Just in Time versus Just in Case
The choice studied in lean production [Lean production] directly influences inventory holdings.
Just in Time
Aims to minimise inventory while still having enough available to meet demand.
Potential consequences:
lower inventory holdings
less cash tied up
less storage and potentially less waste
greater dependence on reliable and timely supply.
AQA's 2025 assessment recognised these benefits in a food-retailing context.
Just in Case
Keeps additional inventory in case it is required.
Potential consequences:
greater protection from unexpected demand
greater protection from supply disruption
higher inventory holdings
greater inventory-related costs.
The optimal approach depends on the business context.
Inventory decisions involve trade-offs
Holding more inventory
Potential benefits:
lower risk of running out
protection against supplier delays
greater ability to meet unexpectedly high demand.
Potential difficulties:
cash tied up
storage costs
risk of waste
inventory may lose value.
Holding less inventory
Potential benefits:
less cash tied up
lower storage requirements
less risk of waste
greater operational efficiency where inventory had been excessive.
Potential difficulties:
greater risk of shortages
stronger dependence on suppliers
less protection from unexpected increases in demand.
The best inventory level is therefore not necessarily the lowest inventory level.
Inventory management and competitiveness
Effective inventory management can affect competitiveness through both costs and customer service.
Cost route
lower unnecessary inventory
↓
less storage and waste
↓
lower costs
↓
greater ability to compete on price or maintain stronger margins
Customer route
sufficient inventory available
↓
customer demand can be satisfied
↓
fewer products unavailable
↓
customer satisfaction protected
↓
competitive position may improve
A business therefore needs to balance inventory efficiency with availability.
Inventory management and Just in Time
AQA's 2025 Paper 2 provides a useful applied example.
Seebus plc used JIT inventory management. The mark scheme recognised that JIT could:
minimise inventory while maintaining sufficient stock
reduce waste involving fresh food
contribute to lower costs
support competitiveness
work alongside software coordinating inventory management with other activities and supply-chain partners.
This is important because good inventory management is not simply about drawing charts.
Managers use inventory information as part of operational decision making.
Inventory management and technology
AQA's operational-management specification explicitly identifies inventory control as one way technology can affect operational decisions and activities. This was explored in technology and operational efficiency [Technology and operational efficiency].
Technology may provide managers with more timely information about:
inventory levels
customer demand
the need for new orders.
The possible chain is:
better inventory information
↓
managers make more informed ordering decisions
↓
less unnecessary inventory or fewer shortages
↓
greater operational efficiency
Technology itself does not remove the need for good decisions. Managers still need appropriate re-order levels, buffer inventory and quantities.
Inventory management and suppliers
Inventory decisions cannot be separated completely from supplier decisions.
For example:
reliable supplier + short lead time
may allow:
lower buffer inventory
Whereas:
unreliable supplier + long lead time
may require:
greater protection through inventory holdings.
The next lesson, choosing suppliers [Choosing suppliers], examines the relationship between supplier decisions and:
cost
quality
reliability
competitiveness.
Inventory management and the supply chain
Inventory moves through relationships between businesses.
Managers therefore need to coordinate:
inventory requirements
suppliers
ordering
deliveries.
This leads directly into supply-chain management [Supply-chain management].
Effective inventory management may become difficult if the wider supply chain is disrupted.
AQA's 2022 Paper 2 used a case where the sudden closure of a vital component supplier disrupted a manufacturer's supply chain and prevented it from finding alternative supplies quickly enough to fulfil all existing orders.
This illustrates why inventory decisions should take account of supply risk.
Inventory management under supply disruption
Suppose a manufacturer normally keeps only a small buffer.
Its supplier unexpectedly stops operating.
The business may face:
normal supplier unavailable
↓
replacement supply cannot be obtained within normal lead time
↓
buffer inventory is exhausted
↓
production is interrupted
↓
customer orders cannot all be fulfilled
A larger buffer could have provided more time to respond.
However, maintaining that larger buffer every day would have created additional costs before the disruption occurred.
This is an excellent evaluation trade-off:
The appropriate buffer level depends partly on the probability and consequence of supply disruption compared with the cost of holding additional inventory.
Changing the re-order level
Suppose demand is increasing.
Previously:
daily usage = 200 units
lead time = 5 days
buffer = 500 units.
Inventory required during the lead time:
200×5 = 1,000 units
If the business wants to retain its 500-unit buffer:
1,000+500 = 1,500
A sensible re-order level in this simplified situation would therefore be 1,500 units.
Now suppose daily use increases to 300 units while lead time and buffer remain the same.
Inventory used during lead time:
300×5 = 1,500
Allowing for the 500-unit buffer:
1,500+500 = 2,000
The business would need to order earlier to maintain the same protection.
📌 The AQA specification does not prescribe a formula for calculating re-order levels. This example simply shows how the concepts relate.
Changing the lead time
Suppose:
daily inventory use = 250 units
buffer = 500 units.
Lead time of 4 days
Expected use during lead time:
250×4 = 1,000
Including buffer:
1,000+500 = 1,500
Lead time rises to 8 days
Expected use during lead time:
250×8 = 2,000
Including buffer:
2,000+500 = 2,500
A longer lead time means more inventory must be available after the order is placed.
This is why lead time can influence the re-order level.
Changing the buffer level
Suppose management raises buffer inventory from:
500 units
to 1,500 units.
This provides an additional 1,000 units of protection.
Possible benefit
If demand rises unexpectedly by 800 units, the additional inventory can help satisfy that demand.
Possible difficulty
The business now routinely holds an extra 1,000 units that may not normally be required.
Whether this is worthwhile depends on:
cost of inventory
supplier reliability
demand uncertainty
consequences of running out.
Changing the re-order quantity
Suppose a business currently orders 10,000 units every time it re-orders.
Managers are considering reducing this to 4,000 units.
Potential benefit
smaller deliveries
↓
lower average inventory
↓
less cash tied up
↓
lower storage or wastage costs
Potential difficulty
smaller deliveries
↓
orders may need to be placed more frequently
↓
business becomes more dependent on frequent successful deliveries
The value depends partly on suppliers and lead time.
Interpreting changes on an inventory-control chart
AQA can require you to work out how a change affects the shape of the chart.
Demand increases
Inventory is used faster.
Therefore:
downward slope becomes steeper
re-order level is reached sooner.
Demand falls
Inventory is used more slowly.
Therefore:
downward slope becomes flatter
it takes longer to reach the re-order level.
AQA's 2023 Paper 1 tested exactly this skill. Most students correctly showed the new delivery but some failed to adjust the downward slope accurately when demand changed.
Re-order quantity increases
A larger delivery arrives.
Therefore:
vertical increase becomes larger
maximum inventory after delivery is likely to be higher if other factors remain unchanged.
Re-order quantity decreases
A smaller delivery arrives.
Therefore:
vertical increase becomes smaller.
The 2023 Paper 1 question required students to represent a re-order quantity that was half the size of the previous delivery.
Lead time increases
If the order is placed at the same re-order level:
the business waits longer for the delivery
inventory falls further before the replacement arrives.
If the buffer is insufficient, the business may run out.
Managers may respond by raising the re-order level.
Buffer inventory increases
The minimum planned level rises.
This gives greater protection but normally increases average inventory holdings.
Analysing an inventory-management decision
A weak response might say:
Holding less inventory reduces costs.
A stronger chain is:
business reduces average inventory holdings
↓
less warehouse space may be required
↓
storage costs fall
↓
less cash is tied up in unsold inventory
↓
operational efficiency and cash flow may improve
But a balanced analysis adds:
lower inventory holdings
↓
less protection from unexpected demand or delayed deliveries
↓
greater risk of running out
↓
production or sales may be disrupted
↓
customers may buy from competitors
The best inventory decision balances both.
Inventory decisions and different business contexts
Fresh-food retailer
Likely considerations include:
inventory may be wasted if held too long
customer demand must still be satisfied
frequent reliable deliveries can make low inventories more practical.
AQA's 2025 Seebus assessment directly used this context.
Manufacturer dependent on a vital component
Likely considerations include:
production may stop if the component is unavailable
supplier reliability is important
buffer inventory may provide protection
larger buffers create additional inventory costs.
AQA's 2022 DT case showed the serious consequences that supplier disruption can have where alternative supplies cannot be obtained quickly.
Business with unpredictable demand
A larger buffer may be valuable because actual demand can exceed forecasts.
However, managers must decide whether the protection justifies the cost of routinely holding more inventory.
Business with reliable, fast suppliers
A shorter lead time and strong reliability may make lower inventory holdings more practical.
This may support a JIT approach.
A method for interpreting an inventory-control chart
Step 1: Read the axes
Normally:
vertical axis = inventory level
horizontal axis = time.
Step 2: Identify maximum inventory
Find the highest inventory level after a delivery.
Step 3: Identify the buffer level
Find the minimum planned level.
Step 4: Identify the re-order level
Find the inventory level at which the new order is placed.
Step 5: Identify lead time
Measure the period between:
order being placed → inventory arriving
Step 6: Calculate the re-order quantity
Use the size of the vertical inventory increase.
Step 7: Examine the downward slope
Ask:
how quickly is inventory being used?
has demand increased or fallen?
Step 8: Include units
If the question asks for:
lead time, give days, weeks or the relevant time unit
inventory quantity, give units
rate of use, give units per day or the relevant period.
This final step sounds small but has repeatedly cost students marks.
Key Words 🔑
Key word | Student-friendly definition | How it may be used in an exam |
Lead time | The time between placing an inventory order and receiving it. | Read or calculate the waiting period from an inventory-control chart and analyse its effect on inventory holdings. |
Re-order level | The inventory level at which the business places a new order. | Identify when replenishment should be ordered and relate this to lead time and usage. |
Buffer inventory | The minimum inventory held to provide protection against uncertainty such as higher demand or delayed supply. | Analyse the trade-off between protection from shortages and the cost of holding extra inventory. |
Re-order quantity | The amount of inventory ordered each time a replenishment order is made. | Calculate the size of a delivery from an inventory-control chart and analyse the effect of larger or smaller orders. |
Inventory-control chart | A graph showing how inventory levels change over time as inventory is used and replenished. | Interpret demand, deliveries, lead time, buffer levels and re-order decisions. |
Hints from the Examiner Reports 💡
Examiner hint: Know what lead time means before trying to calculate it. In the 2022 Paper 2, students who struggled with the chart could have gained credit by demonstrating their understanding of the term.
Examiner hint: Show your working when reading values from an inventory-control chart. The 2022 report noted that students often gave no workings, which meant examiners could not award process credit when a figure had been misread.
Examiner hint: Always include the correct units. Students lost marks in 2022 by giving a numerical lead-time answer without days, a re-order quantity without units, or inventory usage without units per day.
Examiner hint: Do not confuse the re-order level with the buffer inventory level. This was a common error in the 2022 re-order quantity calculation.
Examiner hint: Understand what the slope means. In the 2023 inventory-control-chart question, most students correctly represented the delivery, but many plotted the subsequent downward inventory line inaccurately when demand changed.
Examiner hint: Apply inventory systems to the actual business. In 2025, many students understood JIT but some lost effectiveness by discussing manufacturing when the case was about a retailer.
Common Mistakes ⚠️
Mistake: Confusing lead time with re-order level
Why this is incorrect: Lead time is a period of time.
Re-order level is an amount of inventory.
How to improve: Remember:
lead time = when/how long
re-order level = how many units remain when the order is placed.
Mistake: Assuming the re-order level is when the delivery arrives
Why this is incorrect: The re-order level is when the business places the order.
Delivery occurs later, after the lead time.
How to improve: Follow the sequence:
re-order level reached → order placed → lead time → delivery arrives.
Mistake: Confusing re-order level with re-order quantity
Why this is incorrect: The re-order level tells the business when to order.
The re-order quantity tells it how much to order.
How to improve: Use this memory aid:
level = trigger
quantity = delivery amount.
Mistake: Using the re-order level instead of the buffer level when calculating re-order quantity
Why this is incorrect: On the 2022 AQA chart, the delivery arrived when inventory was at the buffer level, so re-order quantity was:
6,000−750 = 5,250
Students who used the re-order level obtained the wrong figure.
How to improve: Measure the actual vertical increase when the delivery arrives.
Mistake: Assuming buffer inventory should always be zero
Why this is incorrect: A low buffer reduces inventory costs but gives less protection against delayed supply or unexpected demand.
How to improve: Balance:
lower holding costs
against:
risk of running out of inventory.
Mistake: Assuming more inventory is always safer and therefore better
Why this is incorrect: Larger inventory holdings can tie up cash and increase storage or wastage costs.
How to improve: Judge whether the protection provided by additional inventory is worth its cost.
Mistake: Assuming lower inventory always improves efficiency
Why this is incorrect: If inventory becomes too low, production or sales may be disrupted.
How to improve: Use conditional reasoning:
Lower inventory can reduce costs provided the business still has sufficient inventory to meet operational requirements and demand.
Mistake: Getting the slope direction wrong
Why this is incorrect: When demand falls, inventory is used more slowly.
Therefore, the inventory line should become less steep, not steeper.
How to improve: Think:
faster usage = steeper fall
slower usage = flatter fall.
Mistake: Forgetting the units
Why this is incorrect: "4" is not a complete lead-time answer if the correct answer is four days.
How to improve: Write:
4 days
5,250 units
350 units per day.
AQA explicitly identified this problem in the 2022 examiner report.
Exam-Style Questions ✍️
Question 1
Which one of the following best defines lead time?
A. The amount of inventory ordered each time
B. The minimum inventory held
C. The time between placing an order and receiving it
D. The inventory level at which an order is placed
[1 mark]
Answer: C.
Question 2
A business places an inventory order when its stock reaches 2,400 units. The delivery arrives five days later.
Identify:
a) the re-order level
b) the lead time.
[2 marks]
Answer:
re-order level = 2,400 units
lead time = 5 days.
Question 3
A manufacturer has 900 units of inventory immediately before a delivery. Immediately after the delivery it has 6,400 units.
Calculate the re-order quantity.
[2 marks]
Answer:
6,400−900 = 5,500
Re-order quantity = 5,500 units
Mark scheme:
1 mark for correct method.
1 mark for 5,500 units.
Question 4
A business uses 400 units of inventory each day. Its supplier's lead time is six days.
Explain why an increase in lead time could affect the business's re-order level.
[4 marks]
Indicative answer:
If lead time increases, the business must wait longer after placing an order before replacement inventory arrives. Inventory will continue to be used during the longer waiting period, so the business may need to place the order when it has more units remaining. The re-order level may therefore need to increase to reduce the risk of running out.
Question 5
GreenFresh Ltd sells fresh food. Its managers are considering reducing its buffer inventory.
Analyse one benefit to GreenFresh Ltd of reducing its buffer inventory.
[9 marks]
Indicative content:
A lower buffer means GreenFresh normally holds less inventory.
Fresh food may become unusable if held too long.
Lower inventory may therefore reduce wastage.
Less storage may also be required.
Less cash is tied up in inventory.
Operating costs may fall.
This could improve efficiency or gross profit margins.
However, lower buffer inventory provides less protection if demand is unexpectedly high or a supplier delivery is late.
Mark guidance:
Higher-level responses should apply the argument to fresh food and develop the inventory decision into a business consequence.
Question 6
ComponentPro Ltd relies on one supplier for an essential component.
The supplier's lead time has increased from 3 days to 8 days and recent deliveries have sometimes been late.
Analyse why ComponentPro Ltd might increase its buffer inventory.
[9 marks]
Indicative content:
Lead time has increased by five days.
ComponentPro must therefore wait much longer for replacement components.
Recent late deliveries also make the exact delivery time less reliable.
If the essential component runs out, production could be interrupted.
A larger buffer gives ComponentPro more components to use during a delay.
This reduces the risk that production stops.
Customers may therefore be more likely to receive orders on time.
However, ComponentPro will have more cash tied up in inventory and may face greater storage costs.
Question 7
The following information relates to an inventory-control system:
maximum inventory immediately after delivery = 8,000 units
buffer inventory = 1,000 units
re-order level = 3,100 units
order placed on day 14
replacement inventory arrives on day 20.
Calculate:
a) lead time
b) re-order quantity.
[4 marks]
Answer:
a) Lead time
20−14=6
6 days
b) Re-order quantity
8,000−1,000 = 7,000
7,000 units
Mark scheme:
2 marks for 6 days.
2 marks for 7,000 units.
Question 8
StyleHub Ltd currently orders 12,000 units of inventory at a time. Managers are considering reducing the re-order quantity to 5,000 units and ordering more frequently.
Analyse one advantage and one disadvantage of this decision.
[9 marks]
Indicative advantage:
Smaller deliveries mean StyleHub holds less inventory on average.
Less cash may therefore be tied up.
Storage requirements may fall.
This may reduce operating costs and improve cash flow.
Indicative disadvantage:
StyleHub will need more frequent deliveries.
The business becomes more dependent on reliable and timely supply.
A late delivery could cause inventory to run out.
This may result in lost sales or customer dissatisfaction.
Higher-level responses should link the change in re-order quantity directly to the consequences for StyleHub.
Question 9
FreshMarket Ltd operates 40 food stores.
It currently keeps relatively high levels of buffer inventory.
Managers are considering reducing inventory holdings because:
annual storage costs are £900,000
£3.2 million is currently tied up in inventory
8% of its fresh inventory is wasted before being sold
its main suppliers normally deliver within one day
suppliers have achieved 98% of deliveries at the agreed time
customer demand sometimes increases unexpectedly.
Assess whether FreshMarket Ltd should reduce its inventory holdings.
[16 marks]
Arguments supporting lower inventory may include:
£3.2 million is currently tied up in inventory.
Reducing inventory may therefore release cash for other uses.
Annual storage costs are £900,000, so lower holdings may provide significant cost savings.
8% of fresh inventory is wasted before sale.
Lower inventory could reduce this wastage.
Suppliers normally deliver within one day, indicating a short lead time.
98% of deliveries arrive as agreed, suggesting relatively reliable suppliers.
These factors make lower buffer levels less risky and could support a more JIT approach.
Arguments for retaining a buffer may include:
Customer demand sometimes increases unexpectedly.
Lower inventory provides less protection when demand rises.
Even a 98% delivery record means some deliveries do not arrive as agreed.
Because FreshMarket is a retailer, insufficient inventory could mean products are unavailable to customers.
Customers may purchase from competitors.
The financial benefit of lower inventory could therefore be offset by lost sales.
Evaluation:
The data provide a strong case for reducing inventory because FreshMarket faces substantial storage costs, has £3.2 million tied up and wastes 8% of its fresh stock. Its one-day lead time and 98% supplier reliability also make lower holdings more practical.
However, managers should not necessarily eliminate the buffer. Unexpected customer demand and the remaining risk of delayed deliveries mean some protective inventory may still be valuable.
A justified conclusion could therefore be that FreshMarket should reduce rather than eliminate its buffer inventory, with the optimal reduction depending on how costly shortages are compared with the £900,000 storage cost and existing wastage.
Question 10
"Reliable suppliers are the most important influence on how much inventory a business should hold."
To what extent do you agree?
[25 marks]
Indicative content:
Arguments supporting the statement:
Reliable suppliers reduce the risk of delayed deliveries.
Businesses can therefore operate with lower buffer inventory.
Lower inventory may reduce storage costs.
Less cash is tied up.
Reliable suppliers are especially important for JIT systems.
AQA has explicitly recognised that businesses wishing to keep buffer inventory low require reliable suppliers.
Unreliable supply may force a business to hold more protection against disruption.
Arguments challenging the statement:
Other influences may be more important, including:
lead time
predictability of demand
rate of inventory usage
nature of the product
risk of waste
storage costs
availability of storage space
cash available
purchasing advantages from larger orders.
For a fresh-food retailer, avoiding waste may be particularly important.
For a business dependent on a vital component, avoiding production stoppages may be more important.
Evaluation:
Supplier reliability is particularly important when a business wants to operate with low inventory because delays can rapidly cause shortages. This makes it central to JIT systems.
However, it cannot determine inventory holdings on its own. Even a perfectly reliable supplier may have a long lead time, requiring the business to order well in advance. Similarly, highly unpredictable demand may justify a buffer even where suppliers are reliable.
The strongest judgement is therefore that the amount of inventory held should reflect the combined risk created by demand, lead time and supply reliability, balanced against the financial and operational cost of holding inventory.
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