Operations case interviews: a framework for cost, capacity and process

A framework for operations case interviews: cost reduction, capacity, bottlenecks and process improvement, with the formulas and a worked example. 7 min readUpdated 12 November 2026By the Prepper team

An operations case asks how to do the same thing cheaper, faster or with fewer mistakes. Typical questions are "cut costs by 10%", "raise output without a new plant" and "why are deliveries late". They are common at Kearney, Oliver Wyman, the Big Four and in McKinsey and BCG operations practices.

The framework

Step	Question	What to ask for
1. Map	What are the steps or the cost lines?	Process flow, cost base by line
2. Measure	How long, how much, how often at each step?	Times, volumes, unit costs
3. Compare	Against the best site, last year or a competitor	Benchmarks
4. Find the cause	Why is this step slow or expensive?	Price, quantity, mix, waste, waiting
5. Fix and size	What does each fix save, and what does it cost?	Savings, investment, time

Cost reduction: price times quantity

Every cost is a price paid times a quantity used. Ask both questions for each line:

Price: can we pay less? Fewer suppliers, tenders, different specification.
Quantity: can we use less? Less scrap, better planning, fewer hours.

Start with the largest line. A 3% saving on half the cost base beats a 20% saving on a line that is 2% of cost.

Capacity: find the bottleneck

Output is set by the slowest step. Improving any other step changes nothing.

Formula	Use
Capacity = time available / time per unit	Units a step can handle
Utilisation = demand / capacity	How busy a step is
Throughput time = sum of step times plus waiting	How long one unit takes

Worked example

A packaging maker needs €20m more profit on a €480m cost base. Paper is €250m, or 52% of cost. Using four suppliers in place of twelve cuts paper prices 3%: €7.5m. Bringing scrap from 8% to the best plant's 6% saves about €5m. Route planning saves 6% of €50m logistics: €3m. That is €15.5m, so €4.5m must still come from energy and overhead. Try it as a full case.

Mistakes

Listing ideas before asking for the cost breakdown.
Cutting cost in ways that hurt quality or delivery without saying so.
Forgetting the cost and time needed to deliver the saving.

Frequently asked questions

What is an operations case interview?
A case about improving how a company runs: lowering cost, raising capacity, shortening lead times or reducing errors.
Which firms ask operations cases?
Kearney, Oliver Wyman, the Big Four and the operations practices of McKinsey, BCG and Bain ask them most often, but any firm can.
How do I find the bottleneck in a case?
Work out the capacity of each step as time available divided by time per unit. The step with the lowest capacity limits the whole process.

What is an operations case interview?

A case about improving how a company runs: lowering cost, raising capacity, shortening lead times or reducing errors.

Which firms ask operations cases?

Kearney, Oliver Wyman, the Big Four and the operations practices of McKinsey, BCG and Bain ask them most often, but any firm can.

How do I find the bottleneck in a case?

Work out the capacity of each step as time available divided by time per unit. The step with the lowest capacity limits the whole process.