Reviewed: 9 October 2026
Case interview preparation means practising how to investigate a problem, use the available evidence and explain a recommendation. Memorising a list of frameworks is less useful if you cannot define the decision or check the units in your calculation. A case also gives you a chance to notice what the data does not establish.
This guide contains a complete original numerical case with worked answers and changed-input exercises. The fictional business, figures and dialogue are teaching material. They are not a copied consulting firm's case, an actual business forecast or financial advice. Confirm your own assessment format and permitted tools with the recruiting organisation.
First confirm whether your assessment uses cases
A case format is not a universal requirement for every consulting, banking, product or graduate role. Bain's interviewing guidance describes a process tailored to roles and identifies case interviews particularly with consulting positions. Use the actual invitation and employer's current preparation material to establish what applies to your application.
Questions worth clarifying include whether the exercise is spoken or written, individual or group-based, and whether it has a specified time limit. Ask about permitted calculators, notes, software and other assistance rather than assuming that a tool used during preparation is allowed during an assessment. A practice partner can supply missing case facts; during a real interview, ask the interviewer.
An original case: a short stationery finishing run
Decision: A fictional small workshop is considering one limited stationery finishing run. The owner asks whether the supplied order volume covers the costs specified for that run, and what would happen if the selling price changed. The owner has not authorised the run.
The exercise supplies these facts:
| Input | Supplied value | Meaning in this exercise |
|---|---|---|
| Selling price | ₹120 per completed unit sold | Revenue per sold unit |
| Variable cost | ₹70 per completed unit sold | Cost that scales with those units |
| Attributable fixed cost | ₹1,200 for the run | Paid once if the run takes place |
| Capacity | 40 units for the run | Maximum completed units available to sell |
| Base order volume | 30 units | Supplied exercise volume, not inferred from enquiries |
For the calculation, assume every unit in the supplied order volume is completed, sold and paid for during the run. There is no opening stock, unsold production or refund. The supplied ₹70 includes all variable costs considered in this model; the ₹1,200 is the only fixed cost included. Taxes, financing, other overheads and other commercial risks are outside the exercise. Therefore the answer is a balance after the specified costs, not an audited net-profit figure.
These assumptions are part of the teaching case. In a real decision, check them rather than importing them silently.
Clarify the question before calculating
A useful opening is: “I will check whether revenue from 30 supplied units covers the specified variable and fixed costs within the 40-unit capacity. I will then test the lower-price scenario. Is that the decision you want me to address?”
If the interviewer instead asks for a market launch recommendation, the supplied table is incomplete. You would need evidence about achievable paid demand, customer requirements, omitted costs and delivery feasibility. Naming that missing information is more accurate than inventing a market size.
You can structure the limited problem into three parts: contribution per unit, total balance at the specified volume, and sensitivity to price and volume. This structure follows the actual question. It does not require you to recite every business framework you have learned.
Work the base case step by step
Contribution per unit is selling price minus the variable cost attached to that sold unit:
₹120 − ₹70 = ₹50 per unit.
At 30 units, revenue is 30 × ₹120 = ₹3,600. Variable costs are 30 × ₹70 = ₹2,100. Contribution is ₹3,600 − ₹2,100 = ₹1,500. Subtract the supplied fixed cost: ₹1,500 − ₹1,200 = ₹300.
The supplied volume fits the capacity because 30 is no more than 40. Under these assumptions, the base run covers the specified costs and leaves ₹300. This is a conditional model result. It does not prove that 30 paid orders will occur or that the run covers costs excluded from the model.
A concise explanation aloud would be: “Each sold unit contributes ₹50 toward the ₹1,200 fixed cost. Thirty units contribute ₹1,500, leaving ₹300 after that fixed cost. The volume is within the stated capacity.”
Calculate break-even and check feasibility
With positive contribution, break-even volume for this simplified model is fixed cost divided by contribution per unit:
₹1,200 ÷ ₹50 = 24 units.
At 24 units, revenue is ₹2,880 and variable cost is ₹1,680. The ₹1,200 contribution exactly covers the ₹1,200 fixed cost, leaving ₹0. At 23 units, contribution is ₹1,150 and the balance is −₹50. That neighbouring check helps catch an arithmetic or rounding mistake.
The required 24 units are within the 40-unit capacity. If division had produced a fractional unit and only whole units could be sold, the minimum covering volume would need rounding upward. If contribution were zero or negative while the fixed cost remained positive, selling additional units would not produce a feasible break-even volume through this formula.
Adapt when the interviewer changes the inputs
First change only the volume from 30 to 32 units, retaining the ₹120 price. Contribution becomes 32 × ₹50 = ₹1,600, and the balance is ₹400. Capacity still permits the volume. You do not need to rebuild the whole calculation when only one input changes.
Next retain 32 units but reduce price to ₹100. Variable cost remains ₹70. Contribution falls to ₹30 per unit. Revenue is ₹3,200; variable costs are ₹2,240; contribution is ₹960. After fixed costs, the balance is −₹240.
At that ₹100 price, break-even is ₹1,200 ÷ ₹30 = 40 units. That exactly matches capacity. At 40 units, revenue is ₹4,000, variable cost is ₹2,800, and the balance is ₹0. There is no capacity headroom to earn a positive balance at this price under the supplied model.
| Scenario | Units | Price | Contribution per unit | Balance after specified costs |
|---|---|---|---|---|
| Base | 30 | ₹120 | ₹50 | ₹300 |
| Higher supplied volume | 32 | ₹120 | ₹50 | ₹400 |
| Lower price at that volume | 32 | ₹100 | ₹30 | −₹240 |
| Lower-price break-even | 40 | ₹100 | ₹30 | ₹0 |
A lower price does not automatically create the additional paid demand required. Customer enquiries, survey responses and page views are different from paid units. Do not substitute one measure for another without evidence.
Give a recommendation that fits the evidence
An original practice answer is:
“Under the supplied assumptions, the 30-unit run at ₹120 covers the specified costs and leaves ₹300. Break-even is 24 units, within capacity. I would not support a price reduction to ₹100 on the 32-unit scenario: it leaves a ₹240 deficit, and break-even would require the full 40-unit capacity. Before the owner decides to proceed, I would confirm paid order volume, the completeness of the cost inputs and delivery feasibility. The calculation does not establish demand or cover excluded costs.”
This answer gives the result, a comparison and the information needed for a decision. It does not say the owner approved production. An interviewer might challenge an assumption; respond by updating the model or stating what cannot yet be answered.
A repeatable practice session
Read the prompt once and write the decision in a sentence. Identify each supplied number and its unit. Explain a short structure before doing arithmetic. Work the base case, check the result through another route, and finish with a conditional recommendation.
For this exercise, revenue minus all specified costs and contribution minus fixed cost should both give ₹300. If they differ, trace the input or arithmetic error before presenting a conclusion. Have a partner change only one input at a time and ask you to explain which parts of the answer change.
Keep a record of the actual error you made: unclear objective, mixed units, omitted fixed cost, impossible capacity or an unsupported demand assumption. Choose the next practice task around that error. A count of completed cases alone does not show whether your reasoning improved.
Questions people ask
Must I use a named framework?
Use a structure that addresses the decision. Here, unit economics and capacity answer the specified question. A memorised structure can be a prompt, but unrelated sections add work without resolving the case.
What if I make a calculation mistake?
Correct it explicitly and update the conclusion if necessary. For example, forgetting the ₹1,200 fixed cost would incorrectly present ₹1,500 as the final base balance. Show the corrected ₹300 and explain the missing step.
How long should I prepare?
There is no guaranteed preparation period or universal accuracy target. Use the confirmed assessment format, your starting skills and the errors observed in practice. Revisit a weak calculation or explanation rather than promising that a particular number of weeks will secure an offer.
Sources and related practice
Bain's case-interview preparation page describes structured business problem discussions and emphasises clarifying the problem, explaining thinking and adapting to information. The stationery exercise here is independently authored; it is not one of Bain's practice cases.
Use SQL interview practice for a separate technical dataset exercise. For opening an interview, see tell me about yourself sample answers. Confirm which preparation topics actually belong to your own role.