Case Interview Prep: A 6-Week Plan for Undergrads

A good case interview prep plan balances three things: studying on your own, practicing live cases with a partner, and getting honest feedback on every case. The plan here spreads them over six weeks at eight to ten hours a week, so it fits around a full course load.

I'm Stephen Turban, founder of WSG and a McKinsey & Company and Harvard alum. I went through McKinsey's on-cycle recruiting myself, and I've since guided dozens of students through it.

Each week builds one skill on top of the last: the case types, structuring out loud, case math, realistic pressure, your target firm's format, and finally full mock interviews.

For the practice-heavy middle weeks of the plan, these free case resources here cover most of what you need without paying for a course. If you have budget for a paid tool or two, the ones actually worth your time are compared here.

What Case Interviewers Assess

The main thing a case interviewer assesses is how you think through a business problem. Knowing frameworks helps, but only if you can use them on the problem in front of you. McKinsey says it presents a business case "to evaluate your approach to solving complex problems." BCG says "what matters most is how you approach the problem and the quality of your reasoning." In practice, that thinking shows up as five skills:

Structure: how you split a messy question into a few buckets that don't overlap and together cover the problem. The term for that is MECE (mutually exclusive, collectively exhaustive).

Math: how quickly and cleanly you multiply big round numbers, take percentages, find a breakeven, and read a chart.

Insight: spotting the drivers that aren't obvious and explaining why they matter to the client.

Communication: how you phrase your answer, usually the answer first and then the reasons, so your recommendation can be repeated in one go.

Pressure response: how well you adjust when the interviewer pushes back or hands you new data.

How Many Live Cases You Need

Plan on 20 to 24 live cases over the six weeks, spread across the five common case types: profitability, market entry, M&A, operations, and market sizing. A live case is one where a partner reads you the prompt, answers your questions, and pushes back the way an interviewer would. Reading cases on your own is a good way to learn the types, but only a live case trains you to think out loud while someone listens and interrupts, which is what the interview tests. That's why the plan starts with study, adds live cases in week 2, and peaks at six to eight in week 4.

Who to Practice With

Line up two kinds of practice partners before week 2: a regular partner for most of your cases, and someone experienced who has recruited before. Your regular partner, such as a friend or a case club member who's also recruiting, gives you the volume and the honest feedback you need every week. The experienced partner, such as an alum or a case club senior with an offer, knows what a real interview feels like and can tell you whether your approach would hold up in one, which is why they come in for the full mock interviews in week 6. If you can't find a regular partner on campus, PrepLounge's case library has a Meeting Board where candidates schedule mock interviews with each other.

Week 1: Learn the Five Case Types on the Firms' Own Cases

Hours: 8

Live cases: none yet

Spend week 1 learning what question each of the five case types asks and how to start on it, using the practice cases the firms publish. Each type presents a different business problem, so learn to reason from the question each one asks, which works even on prompts a memorized framework doesn't fit:

Profitability: asks why a company's profits changed. Break revenue into price and sales volume, and costs into fixed and variable costs.

Market entry: asks whether a company should enter a new market, whether it would be profitable there, and how it should enter.

M&A: asks whether one company should buy or merge with another. Start from why the client wants the deal, then look at the target's industry and the target itself (how profitable it is, what it's worth, and what combining the two would add), and finally whether the deal is feasible.

Operations: asks how a company can improve the way it runs, such as its supply chain, production, or staffing, to raise output or cut costs.

Market sizing: asks you to estimate a number you aren't given, such as a product's annual sales, by breaking it into pieces you can make assumptions about.

Pay particular attention to profitability, because the same revenue and cost split shows up inside other types, such as whether a market entry would be profitable.

Once you've got the fundamentals, your first cases should be the ones the firms publish, because they're free and they show what each firm expects. Work through the five practice cases on McKinsey's interviewing page, such as Beautify, Diconsa, Electro-Light, and Talbot Trucks. For each one, write your own structure on paper first, then compare it with the firm's answer, so you can see what the firm looked for that you missed. Do the same with the practice cases on Bain's case interview page, Coffee Shop Co. and FashionCo., and read BCG's case interview preparation page.

If you want a book alongside the firm pages, Case in Point by Marc Cosentino covers the case types in one place. Victor Cheng, the author of Case Interview Secrets, teaches hypothesis-driven thinking, where you start with a best guess at the answer and check it against the facts. That habit helps you choose which branch of your structure to look at first.

Start 15 minutes of mental math a day this week and keep it going until the interview. It's a small habit, but it makes the arithmetic in weeks 3 to 6 feel routine. PrepLounge's mental math tool is free with sign-up and has percentage and estimation drills.

Week 2: Build Structures Out Loud

Hours: 9

Live cases: 2

Most of your practice time in week 2 should go to structuring cases out loud. Pick a sample business problem, give yourself two minutes to think through how you'd approach it, then explain your reasoning out loud as if you were speaking to an interviewer. Aim to do this 10 to 15 times during the week, using a mix of the five case types. Saying it out loud matters because in the interview a structure is something you explain, and one that looks clean on paper can come out muddled when you talk it through.

If the question is "A regional grocery chain's profits fell 15 percent last year. Why?" a good structure sounds like this:

"Profit is revenue minus cost, so I'd want to know which side moved. On revenue, I'd split price from volume, and volume into shoppers, trips per shopper, and basket size. On cost, I'd separate fixed costs like rent and store labor from variable ones like cost of goods and shrink, which is inventory lost to theft or spoilage. Can I start with whether revenue has changed?"

The answer starts from the two ways profit can fall (lower revenue or higher costs), so every possible cause sits in exactly one bucket. It then breaks each side into pieces that fit a grocer, such as trips per shopper and shrink, which shows the interviewer you're thinking about this client rather than reciting a generic revenue split. Ending on a question picks the first branch to test and gives the interviewer a chance to hand you data, so you're investigating instead of guessing.

Record a few drills on your phone and listen for buckets that overlap and for filler words, which are hard to notice while you're talking. Then do your first two live cases with your regular partner. Ask your partner to grade only structure and communication this week, so the feedback stays on the skills you're building.

Week 3: Practice Case Math and Market Sizing

Hours: 9 to 10

Live cases: 4

In week 3, practice doing case math out loud: the arithmetic is generally easy, and the skill is keeping it clean while you talk through the business. For big numbers, round, multiply, then adjust. For example, if a market is 320 million people spending $45 a year, say "300 million times 45 is 13.5 billion, and I rounded the population down about 6 percent, so call it a little over 14 billion." Rounding first keeps the multiplication easy enough to do in your head, and naming the adjustment shows the interviewer you know which way your estimate is off.

Market sizing, on the other hand, can be worked top-down, starting from a big known number like population and narrowing it, or bottom-up, starting from what one unit, such as a single store, can do. Many questions use both. Here's how "How many gas stations are there in the US?" combines them, estimating total demand from the population and then dividing by what one station can serve:

• Vehicles: about 340 million people and a little under one vehicle per person gives about 300 million vehicles.

• Demand: if each vehicle fills up about once a week, that's 300 million fill-ups a week.

• One station: ten pumps serving about 30 cars a day each is 300 cars a day, or about 2,100 a week.

• Answer: 300 million divided by 2,100 is about 140,000 stations.

The method is to estimate how much is needed and how much one unit can supply, then divide. That's why the station's capacity deserves as much care as the demand side: if one station served twice as many cars, your answer would halve. NACS, the convenience store trade group, counts about 122,600 convenience stores that sell fuel and about 148,000 fueling outlets in all, so an estimate of 140,000 is the right size. The interviewer cares more about your process than the exact number, so state every assumption, keep the math clean, and say at the end whether your answer feels like the right size.

When a chart lands, take about 30 seconds: read the title, axes, and units, then say the one thing that changed. "This is unit sales by region over five years. The Northeast is down about 20 percent, and it's half the business." Then connect it to your structure and say what it means for the client, because that "so what" is the insight the interviewer is listening for. Ask your partner to include at least one chart and one market sizing in each live case this week.

Week 4: Practice Under Real Interview Conditions

Hours: 10

Live cases: 6 to 8

By week 4, you should be familiar with the main case types and how to approach them. Now it's time to see how well you can apply what you've learned in a realistic setting.

Week 4's live cases should run like real interviews, with a partner who pushes back, adds new information, and doesn't stop the case for feedback. Before each case, hand your partner the prompt and the data they should reveal partway through, so the new information arrives the way it would in an interview. If you realize your first approach isn't working, explain how you'd adjust it and keep going. The goal is to get comfortable thinking on your feet, especially when the conversation doesn't go the way you expected.

Pay particular attention to how you close each case. You can work through the analysis correctly and still struggle to say what it all means. Practice ending with a clear recommendation in about 30 seconds, supported by two reasons, one risk, and a next step. For example: "I'd recommend raising prices by 5 percent on the premium line. Our estimates suggest we'd lose few customers, and margins on those products are twice the average. The main risk is competitors undercutting us, so I'd test the increase in one region before rolling it out."

After each session, spend a few minutes reviewing your performance with your partner. Keep a simple log of where you struggled, whether that was handling an unexpected question, making a calculation, or explaining your recommendation. Look for mistakes that keep coming up rather than treating each case on its own, because those repeats are what you'll work on in the last two weeks.

Week 5: Practice in Your Firm's Format and Prepare Fit Answers

Hours: 9

Live cases: 5 to 6, mostly in your firm's format

In week 5, practice in the case format of the firm on your calendar, because MBB firms tend to run cases differently. A case is either interviewer-led, where the interviewer asks set questions in order, or candidate-led, where you choose what to explore and drive to the answer. The firm-by-firm formats come from the case prep company CaseCoach, because the firms don't publish them, and CaseCoach adds that the style "will depend largely on the preference of your interviewer." So do most of this week's cases in your firm's format and one or two in the other.

McKinsey: cases tend to be interviewer-led, with a set script of questions that you answer in turn: a structure, narrated math, then a synthesis.

BCG: cases tend to be candidate-led. You propose the structure, choose what to explore, and drive to a recommendation, so practice with a partner who has been told to stay quiet.

Bain: CaseCoach reported in 2024 that Bain was moving from candidate-led toward interviewer-led cases, so practice both, and practice the 30-second close until it's routine.

Other firms with strong industry practices: if you're interviewing at a firm like Oliver Wyman, which has a financial services practice, or L.E.K. Consulting, which has a life sciences practice, do at least two cases in that industry, so its economics and vocabulary aren't new to you in the room.

Prepare five fit answers this week, each under 90 seconds: why consulting, why this firm, and a leadership, a failure, and a conflict story. Fit comes in week 5 because your case skills are in place and need fewer hours to maintain. Your "why this firm" answer should name something specific, such as a coffee chat with a consultant in a named practice, a case competition the firm sponsored, or an office event you attended.

If McKinsey is on your list, prepare more than that. Its interviewing page lists four areas and suggests two personal examples for each, and the page lets you preview the questions you'll hear in each area. It asks you to discuss your examples "in a detailed way, focusing on your specific role." It also asks you to "be prepared to have a conversation, not to present a rehearsed story," so treat the 90-second version as the start and know each example well enough to talk through what you did and why.

Week 6: Run Full Mock Interviews and Fix Your Recurring Mistakes

Hours: 8

Live cases: 3 to 4 full mock interviews

Spend your last week on full mock interviews with people you haven't practiced with, so the real interview feels familiar. You've built the skills, and the last step is to see how well they hold up across from an unfamiliar interviewer. This is the week for the experienced partner you lined up earlier and for anyone else you haven't cased with, such as another alum or a new practice partner. Someone new is useful because they won't know your usual approach or give you the cues a regular partner does. Keep each mock as close to the real interview as possible, with both fit questions and a full case in your target firm's format, and set aside time afterward for detailed feedback.

Use that feedback to narrow your preparation. Look back at the mistakes you've logged since week 4 and pick the two that have appeared most often. Spend your remaining practice time on those two instead of working through more new cases, because at this stage fixing a known weakness helps more than extra material.

Finally, take care of the practical details. If your interview is virtual, test your camera, microphone, and internet connection the day before. Keep your workspace clear, have paper and a pen ready, and confirm your target firm's rules on calculators and other materials (McKinsey's practice cases say calculators aren't allowed), so nothing distracts you on the day.

When to Start, and Where to Find This Cycle's Deadlines

Start the plan by the week you submit your applications, or six weeks before your earliest possible first-round interview if that comes sooner, and if that date has passed, start now. The application week matters because some screens come before any interview. BCG invites a select group of US Associate applicants to an online case about two weeks after the application deadline, so your case practice needs to be under way when you apply. The other MBB screens are different:

McKinsey: applicants for most consulting roles take Solve, which McKinsey calls "a gamified assessment that tests your natural problem-solving abilities" and says needs no preparation.

BCG: before the online case, US Associate applicants take the Consultant Career Assessment, which arrives within about 90 minutes of applying.

Bain: some offices, such as London, send a link to an online assessment after you apply. Bain says London's covers numerical aptitude, logical reasoning, and behavioral preferences.

Your first steps can be small: read one McKinsey practice case and write your structure before you look at the answer, message one person who could case with you next week, and put 15 minutes of mental math on tomorrow's calendar.

The next MBB deadlines will appear on the McKinsey, BCG, and Bain careers pages. Last cycle, McKinsey's Business Analyst internship deadline and the first of Bain's two Associate Consultant Intern deadlines were both March 29, 2026, as the Tufts deadline tracker shows. Our consulting recruiting timeline has the full calendar.