Supply Chain Optimization Case Interviews Guide

A supply chain optimization case interview asks you to improve how goods move from suppliers to customers. You diagnose problems in sourcing, production, stock or delivery, then compare solutions on cost, service and risk. The goal is a practical recommendation that improves the whole chain while meeting the client’s constraints.

This guide explains the decisions, calculations and trade-offs behind that recommendation. The worked example and ten practice scenarios are fictional exercises created for interview preparation. Their figures are assumptions for learning, not reported client results.

Start with the service promise

A cheaper supply chain is useful only if it still delivers what customers need. Ask the interviewer to define success before choosing a solution. A retailer might want lower costs while keeping its delivery promise. A spare-parts supplier might instead prioritize availability because a missing part can stop a customer’s factory.

Clarify the scope as well. Does the problem concern one warehouse, a product family or the entire network? Confirm the time horizon and the baseline. A target to release cash this quarter requires a different answer from a plan to cut annual operating costs.

Keep three questions in view throughout the case:

• What outcome must improve, and by how much?
• What service, quality or capacity requirement must still hold?
• Which costs and risks move elsewhere when we change this part of the chain?

For example, fewer warehouses may reduce rent and stock. They may also increase delivery distance and make next-day orders harder to fulfil. Your analysis should compare those effects together.

Map the flow before choosing a framework

Draw the path from suppliers to production, storage and delivery. Add returns when they matter. Mark where products wait, where information changes hands and where demand becomes uncertain. This simple map helps you locate a problem before naming a technology or planning method.

ASCM’s SCOR Digital Standard offers a broader reference for linking supply chain processes and performance. Use it as background for understanding the network; the interview still requires a structure tailored to the client’s decision. ASCM’s SCOR Digital Standard.

Area	Useful evidence	Decision it helps you make
Sourcing	Supplier lead time, defect rate, landed cost and concentration	Whether to change suppliers, terms or buffers
Production	Output, bottleneck capacity, downtime and yield	Whether to improve the process or add capacity
Inventory	Stock by item and site, demand, stockouts and obsolescence	Where to reduce, move or protect stock
Distribution	Cost per order, distance, delivery time and failed deliveries	Whether to change routes, carriers or locations
Planning	Forecast error, bias, promotions and replenishment rules	Whether the planning process explains the mismatch
Returns	Return reasons, recovery value and handling costs	Whether to repair, resell, recycle or prevent returns

Request evidence that separates competing explanations. If delivery performance fell, a monthly freight total is not enough. Ask whether the delay occurs before dispatch, during transport or at the customer’s address.

Choose measures that match the problem

Metrics are useful when their definitions are clear. Ask what each measure includes and keep that definition consistent. A supplier’s on-time measure may refer to dispatch, while the customer measures arrival.

Inventory turnover and days of stock

Inventory turnover equals annual cost of goods sold divided by average inventory at cost. If annual cost of goods sold is $24 million and average stock is $4 million, turnover is six times.

Using a 365-day year, average inventory days are about 61. That average can hide shortages in one product and excess stock in another. Segment before recommending a general stock reduction.

Do not mix sales value with inventory at cost. Also check whether a year-end stock balance is representative. A seasonal business may hold much more stock just before its busiest period.

Service levels and delivery reliability

Define whether the client measures complete orders, order lines or individual units. An order with one missing item can fail an order-level service target even when most units arrive. Keep the denominator consistent when comparing sites or suppliers.

Lead time also needs a start and end point. A supplier’s production time may exclude the queue before production and the journey to the warehouse. Customers experience the full wait.

Capacity and bottlenecks

A process can produce only as fast as its limiting step permits. Suppose cutting can handle 1,200 units a day, assembly 900 and packing 1,100. The line’s maximum throughput is 900 units before allowing for defects or downtime.

Improving packing alone will not lift that limit. First test assembly’s real constraints. Then check whether the next step would become the bottleneck after the proposed change.

Total relevant cost

Compare the costs that change between options. Include procurement, production, storage, freight, quality failures and returns where relevant. Add the effect of lost sales only when the case supports an estimate.

Separate a cash release from an annual expense reduction. Selling down $1 million of stock can release working capital once. It does not create $1 million of recurring annual profit.

Worked case: consolidate two warehouses

A fictional distributor wants to reduce costs without lowering its complete-and-on-time delivery rate below 96%. It currently ships from two warehouses. Management proposes serving the same customers from one site.

The case provides the following steady-state estimates. All amounts use the same currency and annual period, except inventory and transition costs.

Input	Two warehouses	One warehouse
Annual warehouse operating cost	$2.40m	$1.60m
Annual outbound freight cost	$1.20m	$1.55m
Average inventory at cost	$5.00m	$4.20m
Annual holding-cost rate	20%	20%
Complete-and-on-time deliveries	97%	96.5% estimated
One-time transition cost	—	$0.50m

Calculate the recurring benefit

Warehouse costs fall by $800,000 a year. Freight rises by $350,000. The $800,000 stock reduction saves a further $160,000 a year at the stated holding-cost rate.

The estimated recurring benefit is therefore $610,000 a year: $800,000 minus $350,000 plus $160,000. The $800,000 stock release is separate. It must not be added again as annual savings.

Check the holding-cost definition before accepting this result. In this exercise, that rate excludes warehouse expenses already counted in the first row. Otherwise, the calculation could count the same storage saving twice.

Test the investment and service requirement

Simple payback on the $500,000 transition cost is about 0.82 years, or ten months, using the recurring benefit alone. This is a screening calculation. It ignores discounting, tax, the timing of costs and any gradual ramp-up of benefits.

The estimated delivery rate clears the 96% floor by only half a percentage point. That margin is small. Ask for performance by region and during peak demand before accepting the estimate.

If freight increases by another $200,000, the annual benefit falls to $410,000. If service falls below the target, the proposal needs a redesign even if it still saves money. Options might include a regional carrier or a small local stock buffer.

State a conditional recommendation

A useful close would be: “I recommend testing the one-warehouse model. The base case saves $610,000 a year and meets the service floor. The main risk is late delivery to distant customers. I would validate peak-period capacity and pilot those routes before closing the second site.”

That answer links the decision to evidence. It also tells the client what must be true before committing.

Ten supply chain practice scenarios

Use each scenario to practise selecting the next piece of evidence. Avoid giving the same solution to every client. The operating constraint should change your analysis.

1. Electronics inventory across countries

An electronics manufacturer has excess stock in some countries and shortages in others. Start with stock and demand by item and location. Check whether replenishment rules reflect lead times and local sales patterns.

Compare transfers, smaller order batches and different stock buffers. A high-value item is not automatically suited to just-in-time supply. Demand uncertainty, replenishment reliability and the cost of a shortage still matter.

2. E-commerce last-mile delivery

An online retailer faces rising delivery costs and more failed first attempts. Split cost per successful delivery into route cost, stops completed and repeat attempts. Segment dense city routes from distant or hard-to-access addresses.

Compare better address data, delivery windows, pickup points and carrier changes. A lower carrier quote may be worse overall if failed deliveries and claims rise. Define the service promise before trading speed for cost.

3. Pharmaceutical supply resilience

A medicine producer depends on one supplier for a critical input. Map the points of concentration and identify how long a disruption could last. Ask what qualification work a second supplier would require.

Compare a qualified alternative, strategic stock and changes to production planning. Do not assume a supplier can be replaced immediately. The interview analysis should identify the quality and approval constraints that specialists must confirm.

4. Lower-impact transport

A manufacturer wants to reduce freight emissions while protecting its delivery commitments. Compare modes, routes and shipment frequency using a common boundary. Check whether slower transport would require more stock or create additional waste.

Present cost, delivery time and estimated emissions separately. A lighter shipment is not enough to prove a lower total impact. The calculation also depends on distance, mode and how the transport capacity is used.

5. Retail planning technology

A retailer wants a new forecasting system because shelves are often empty. First test stock records, replenishment settings and supplier performance. Better forecasts will not fix an item that is recorded as available but is missing from the shelf.

Propose a pilot on a defined product group. Compare forecast quality, availability and stock levels with the existing process. Include training, data cleanup and ongoing support in the cost case.

6. Fast-fashion responsiveness

A clothing retailer loses sales on popular items and marks down slow sellers. Separate stable basics from trend-driven products. Compare shorter production cycles with larger, cheaper batches.

The right answer may combine both approaches. Use quick replenishment where demand is uncertain and speed has value. Keep an eye on supplier capacity and the extra cost per unit. More frequent orders do not help if the factory cannot respond.

7. Cold-chain reliability

A temperature-sensitive product suffers spoilage during delivery. Identify when the temperature leaves the required range and how long each excursion lasts. Check loading, handovers, packaging and delays.

Compare packaging changes, route design and better monitoring. Sensors may reveal a failure without preventing it. The recommendation needs an operating response when an alert occurs, with ownership and escalation rules.

8. Electronics returns

An electronics company spends too much handling returned products. Segment returns by reason, condition and expected recovery value. Estimate the net value of repair, resale, parts recovery and recycling.

Prioritize a faster decision on each return. A repair process can destroy value if its cost exceeds the resale benefit. Investigate preventable returns as well, such as unclear product information or shipping damage.

9. Automotive supplier disruption

A vehicle producer may lose access to a low-cost component. Map which models use it and how much production depends on it. A cheap part can have a large impact when its absence stops an entire line.

Compare buffer stock, alternate sourcing and production resequencing. Assess shared upstream suppliers before calling two sources independent. A second direct supplier may still rely on the same constrained material or facility.

10. Consumer-goods packaging and network design

A consumer-goods business wants cheaper, lower-impact packaging. Compare the full effects on material cost, packing speed, transport utilization and damage. Ask whether the new pack changes shelf life or customer acceptance.

A packaging saving can disappear if breakage rises. Recommend a test across production, transport and stores. Track total cost per saleable unit rather than material cost alone.

Common mistakes and better responses

Mistake	Why it weakens the answer	Better response
Cut stock everywhere	Some items may already be below their service buffer	Segment by demand, lead time and shortage impact
Recommend software immediately	The cause may be an operating rule or poor data	Diagnose the process before selecting a tool
Add all savings together	Several initiatives may remove the same cost	Reconcile benefits against one baseline
Optimize one site in isolation	Costs or delays may shift elsewhere	Compare end-to-end effects
Give a precise forecast without support	The result depends on uncertain assumptions	Show a range and the assumptions that change the decision

Turn practice into better interview answers

Choose one scenario and sketch a structure without looking at the example analysis. Explain why your first data request matters. Then complete one calculation and state what the answer changes.

Ask a practice partner to introduce a constraint halfway through. The client might need faster delivery, face a spending limit or lose a supplier. Revise your recommendation instead of defending the original plan automatically.

Finish with a short decision, its strongest evidence and the next action. Use the ordered practice method below to repeat the exercise. For more context, explore industry primers and case interview preparation. The sector primers and guides collected under Resources cover the surrounding business context.

Three further supply chain prompts with worked solutions are in real-world supply chain optimization cases, and the case interview preparation hub covers the other formats.