You have practised your cases out loud, your structure holds, your calculations are clean, and the invitation to the second round mentions a "written case study". No more interviewer answering your questions while you analyse: a pack of documents, limited time, a few slides to produce, then a presentation to a consultant. This exercise, called a written case, exists in some firms and for some roles only. This article explains what it tests, how to read a pack without drowning in it, how to sort the data and build slides you can defend, and then how to present them.
What a written case is
A written case is a case interview whose brief and data arrive in written form: a pack of pages or slides, with charts, tables, and sometimes a newspaper extract or an email from the client. The candidate works alone, within a set time, then produces a few slides (on a computer or on paper, depending on the firm) and presents them to an interviewer, who asks questions.
It helps to distinguish this format from two similar exercises:
- the classic oral case, where the interviewer speaks, answers your questions and releases the data as the conversation goes; the article on candidate-led and interviewer-led cases describes these variants;
- online tests, timed and scored by a machine, which our article on consulting firms’ online tests covers in detail.
The written case is a human-assessed exercise: nobody gets an automatic score, and what is evaluated is the quality of your reasoning and the way you defend it.
On the firms’ side, public information is thin and should be read with care. BCG is one of the few to state it plainly: on its page about the recruitment process of the Paris office 🔗, it lists a written case study in the second round, for end-of-studies internships and permanent positions. Its case preparation page 🔗, on the other hand, does not mention a written format: it describes what the firm expects from any case, namely structuring your approach, analysing data, doing quick calculations and communicating clearly. For its part, Bain describes on its interview page 🔗 a written take-home exercise for certain roles, sometimes with a presentation of the result; the page does not say it is a strategy consulting case, so do not assume it is the same exercise. For other firms, only the invitation email or your contact in human resources is authoritative: ask for the format, the duration and the materials allowed.
Reading the pack without getting lost
The main trap is linear reading: you read everything, in order, with the same care, and time runs out before your first idea. A pack is often longer than what can be processed, part of the pages are secondary, and it is sometimes deliberately noisy.
A simple method comes down to four moves.
- Start with the question. First read what the client is asking exactly and what is expected of you (a yes or no recommendation, a choice between options, an action plan). Write it in one line at the top of your sheet; it will be your compass.
- Skim the whole pack before going into detail. Spot the titles, captions, units and sources. In a few minutes you know where the numbers are, where the context is and which pages are only there as a diversion.
- Formulate a hypothesis very early. It may turn out to be wrong. But it gives you a criterion for reading: does this piece of data support it, contradict it, or have nothing to do with it?
- Take notes as you read, not afterwards. For each useful page, one line: what it shows and what it changes for the recommendation. Without this, you will reread everything when it is time to build the slides.
Keep an eye on the clock at every step. In a written format, nobody tells you it is time to move on, and producing the slides always takes longer than planned. Set aside its share from the start.
Sorting the useful data
A good pack contains information that matters, information that is true but has no effect on the decision, and sometimes inconsistencies. Your job is to separate the three.
Keep what weighs on the decision. A piece of data is useful if, by changing it, the recommendation could change. A margin gap between two products that account for almost all revenue matters; a detail about a marginal segment, much less.
Check units and periods. The classic mistakes are here: thousands mixed up with millions, a monthly figure compared with an annual one, different currencies or scopes from one table to another. A chart whose axis does not start at zero can also suggest a larger gap than there really is.
Cross-check rather than pile up. An isolated figure says little; set against another, it becomes a conclusion. Unit cost on one side and price on the other give the margin; a site’s capacity and demand give the utilisation rate. The calculations are usually simple, but they must be done quickly and without error; the article on mental maths in case interviews details the techniques that hold up under pressure.
Flag what is missing. It is normal for a piece of data to be missing to conclude. Say so in your presentation, state the assumption you have retained and explain what you would ask the client to confirm it. A candidate who names their limits looks more solid than one who hides them.
Building three defensible slides
The number of slides requested varies; if you are given the choice, a few well-built slides are better than many vague ones. A three-slide outline suits many packs, and it can be adapted.
- Slide 1, the answer and its context. A title sentence that gives the recommendation, then the two or three reasons that support it. If the interviewer could read only one page, it would be this one.
- Slide 2, the proof. The chart or table that carries the main argument, with a title that says what it shows ("Margin is falling mostly in activity B", not "Margin by activity"). The key figures are readable, the source is given, nothing unnecessary clutters the page.
- Slide 3, the risks and next steps. What could call the recommendation into question, what would need to be checked, what you would do in the following weeks.
A few rules of form, which also apply on paper:
- one message per slide, stated in the title; if someone reads only the titles in sequence, they should understand the whole story;
- little text, rounded figures, clear units;
- a visible hierarchy: the most important figure can be spotted in a second.
It is the same know-how as a consultant’s daily work. Our article on consultant slides details the layout and title principles that apply here in miniature.
The presentation to the interviewer
The second half of the exercise is played out orally, and it weighs as much as the slides. The interviewer has read your pack in the background, knows the traps, and will test the solidity of your reasoning.
To begin, state the answer in your first sentence: "I recommend not launching the project, for three reasons." Then go through your slides in order, without reading them word for word: the title gives the message, you provide the explanation.
Then come the questions, which are the real test. The interviewer might ask where a figure comes from, what would happen if an assumption changed, or why you set aside a given option. A few reflexes help:
- answer first, justify afterwards;
- find the figure in your notes rather than making it up;
- acknowledge an error when it appears, correct it and draw the consequence for the recommendation; this is better perceived than a stubborn defence;
- do not change your recommendation at the first objection: if a new argument really changes the analysis, say so; otherwise, hold your position.
Tone matters as much as content. The firm is looking for a future colleague whom a client will listen to, not a candidate who recites.
Practising with realistic packs
Practice packs are rarer than oral cases, but you can prepare seriously.
- Do the cases from firms’ websites under constraint. Many firms publish sample cases. Read them within a fixed time, then produce three slides instead of simply thinking.
- Work with a partner. One plays the interviewer and asks questions about the slides; the other defends. Our article on practising cases with a partner describes the method.
- Repurpose other documents. An annual report or a sector study can serve as a pack: ask yourself a decision question, give yourself a time limit, produce your slides.
- Time each step. Reading, sorting, calculations, slides, presentation: note where you lose time, and adjust.
- Record yourself presenting. Listening back reveals hesitations, overly long sentences and misquoted figures.
Also prepare what surrounds the exercise. Your CV is reread at every round, and the interviewer may look in it for the link between your experiences and your ease with numbers. The strategy consulting intern CV template shows how to present analyses and quantified results. To put yours in order, the ConseilCV editor handles the layout for you and produces a PDF that applicant tracking systems (ATS) read correctly, which prevents a poorly structured CV from being rejected before a human opens it. To understand where the exercise fits in the whole journey, reread our article on recruitment at BCG.
Frequently asked questions
Do all consulting firms use a written case?
No. The format exists in some firms, some offices and for some roles. BCG states it for the second round of its Paris office, but many other firms stick to oral cases. Always read the invitation and ask for the exact format.
How many slides should I produce?
It depends on the instructions, which must be followed to the letter. Without any indication, aim for few slides: an answer, a proof, and the risks and next steps. One well-argued slide is worth more than five slides repeating the same idea.
Do I need to master PowerPoint to succeed?
Technical mastery helps you save time, but the assessment mostly concerns the content and the structure of the message. If the exercise is on paper, legibility matters more than drawing skill. Practise under the announced conditions.
What if I run out of time to finish the slides?
Deliver a short but coherent version rather than unfinished work. A clear recommendation and a single solid proof are worth more than three half-filled slides. Say out loud what you would have added with more time.
Can I make a calculation error without being eliminated?
An error is not necessarily disqualifying if you spot it, correct it and measure its effect on the recommendation. What hurts is not seeing it, or being stubborn about it. Check your orders of magnitude before putting them on a slide.
Sources
- Boston Consulting Group, Recruitment process of the Paris office (HEC Paris school page) 🔗
- Boston Consulting Group, Case interview preparation 🔗
- Bain & Company, Interview prep: case interview and written assignment 🔗