How to Prepare for an MBB Case Interview in 2026: McKinsey, BCG and Bain Consulting Interview Guide

What is an MBB case interview?

MBB stands for McKinsey, BCG (Boston Consulting Group) and Bain — the three firms widely regarded as the most selective in management consulting. Getting an offer at any of them typically requires clearing three gates:

1. An online screening assessment (different at each firm)

2. A personal fit or behavioural interview

3. Two to three rounds of live case interviews

This guide covers all three, firm by firm, with a 6-week prep plan at the end.

Stage 1: Online screening assessments

McKinsey Solve (2026 format)

McKinsey Solve is a game-based digital assessment taken before first-round interviews. As of mid-2025, McKinsey rolled out a new two-module format globally. If you are still reading guides that describe the Ecosystem Building game as part of Solve, those guides are outdated — Ecosystem Building was phased out.

The current 2026 format has two modules:

• Redrock Study (approximately 35 minutes): an interactive case study set on a wildlife research site. You read exhibits, do calculations (percentages and ratios feature heavily), and draw conclusions under time pressure. The format splits into a Study phase (investigation, analysis, report) and a Cases phase (six shorter cases).

• Sea Wolf (approximately 30 minutes): a logic and optimisation game involving phases of classification and selection under constraints. Introduced as part of the main assessment in spring 2024.

Total time is approximately 65 minutes. McKinsey’s own careers page describes Solve as testing natural problem-solving — they say no preparation is needed, though most candidates disagree given the roughly 20-30% pass rate reported by prep communities.

The most effective preparation involves practising with timed case exhibits (for Redrock) and at least one or two Sea Wolf simulations to avoid pacing shock on test day.

BCG Casey chatbot (2026 format)

BCG’s online screening is called the Casey chatbot, or the BCG Online Case. It replaces the older BCG Potential Test at most offices.

• Format: A chatbot named Casey presents a business case and asks 8-10 sequential questions. You cannot go back once you answer. Question types include how to frame the problem, numerical calculations, exhibit interpretation, estimation, and structured short answers.

• Video recommendation: The final section requires you to record a one-minute video presenting your recommendation. This is timed and cannot be redone.

• Duration: Approximately 25-30 minutes.

• Pass rate: Estimated at 20-30% of candidates pass, making it one of the more selective early-stage filters in consulting recruiting.

Preparation is essentially case interview preparation done alone. Practising full cases with peers and timing yourself on exhibit-heavy problems are the most transferable skills.

Bain SOVA test (2026 format)

Bain uses the SOVA assessment as its online screening tool. Unlike the McKinsey and BCG tests, SOVA is not a case study — it is a psychometric assessment.

• Sections: Numerical reasoning (charts, tables, quantitative data), logical reasoning (pattern recognition, sequencing), situational judgement (workplace scenarios with Most Effective / Least Effective responses), and a personality assessment. As of May 2026, verbal reasoning appears to be phased out — though prep resources still include it in case it is reintroduced.

• Timing: The test is untimed, but your speed on each question is tracked. Your overall score reflects both accuracy and how quickly you answered correctly.

• Duration: Approximately 75 minutes in total.

The key insight is that candidates who rush and make errors score lower than those who are both accurate and efficient. Practise under mild time pressure rather than under strict cut-offs.

Stage 2: The personal fit interview

All three firms run a fit or behavioural round alongside or before their case rounds. McKinsey’s version is the most structured.

McKinsey PEI (Personal Experience Interview)

The McKinsey PEI is a structured behavioural interview with four named dimensions. Each interviewer picks one dimension and probes a single story in depth — expect five to six follow-up questions on the same story.

The four dimensions (note: “Entrepreneurial Drive” was renamed “Drive” in July 2025):

• Drive: Pursuing ambitious goals and overcoming obstacles. What they look for: self-motivation, resilience, exceptional achievement.

• Leadership: Guiding a team or group through a challenge. What they look for: influence, team mobilisation, decision-making under ambiguity.

• Connection: Building trust and relationships with a specific person, often a difficult stakeholder. What they look for: empathy, persuasion, conflict resolution.

• Growth: Learning from failure or feedback and changing your approach as a result. What they look for: self-awareness, intellectual humility, iteration.

Prepare a distinct, detailed story for each dimension. Your opening should take about two minutes. The interviewer will then drill into what exactly you did, why you chose that approach, and what you were thinking at each step. Thin stories fall apart after two follow-ups.

BCG and Bain fit questions

BCG and Bain use more conventional behavioural questions — motivations for consulting, why that specific firm, leadership and teamwork examples. Both expect you to express genuine commercial interest and to tell coherent stories with clear personal contributions.

For Bain, interview format varies by office and role level. Check with your recruiter for the exact structure at your office.

Stage 3: Live case interviews

The live case is the core of the MBB hiring process. Each case runs approximately 30-45 minutes and presents a business problem you must analyse and solve in real time.

McKinsey: interviewer-led

McKinsey cases are interviewer-led. The interviewer controls the pace and tells you what to look at next. You are expected to provide a structured hypothesis, work through exhibits accurately, and synthesise a clear recommendation. Mental arithmetic fluency matters — you will do calculations verbally.

BCG: interviewer-led, exhibit-heavy

BCG cases are also interviewer-led and exhibit-heavy. The interviewer guides the agenda and feeds you data sequentially. BCG places particular emphasis on quickly reading charts and tables, structuring short written answers under time pressure, and closing with a clear, quantified recommendation. BCG interviewers also value creative, lateral thinking alongside analytical rigour.

Bain: candidate-led, with written component

Bain cases are candidate-led. You are expected to drive the structure, hypothesis, and analysis throughout. Some Bain offices include a written case component (particularly for experienced hire rounds) where you analyse a 15-30 slide data packet and present a quantified recommendation. Bain’s close ties to Bain Capital mean private equity due diligence cases appear more often than at McKinsey or BCG.

The 4 most common case types

Profitability: A company’s profits are declining. Diagnose why using the Profit = Revenue minus Cost tree. Segment revenue by volume and price, then costs by fixed and variable. Identify the biggest driver before recommending a fix.

Market entry: Should a company enter a new market? Assess market attractiveness (size, growth, competitive intensity), client capabilities (resources, distribution, differentiation), economics (margins, payback period), and risks.

Growth: How can a company grow revenue? Consider organic options (new products, new segments, pricing) and inorganic options (partnerships, acquisitions). Quantify the opportunity for each lever.

Merger and acquisition: Should a company acquire a target? Assess strategic fit, financial returns (synergies, deal price versus value), integration complexity, and risks.

A simple case structure to anchor every problem

1. Clarify: Restate the problem and confirm the client’s objective. Ask one or two targeted questions.

2. Structure: Set up a framework on paper. State your main branches before diving in.

3. Analyse: Work through each branch systematically. Do mental maths out loud. Ask for data you need.

4. Synthesise: State a clear recommendation with the two or three most important supporting reasons. Acknowledge the main risk.

The recommendation should lead with the answer, not build toward it.

10 worked example questions

These are illustrative of the kinds of problems that appear across MBB live cases. They are not predictions of specific questions.

1. Profitability — setup: A UK supermarket’s operating profit has fallen 15% year on year despite flat revenue. Where do you start?

Start with the Profit = Revenue minus Cost split. Revenue is flat, so the driver is cost. Split costs into cost of goods sold (COGS) and operating expenses. Ask which has changed. If COGS has risen, ask whether it is volume or unit cost. Follow the biggest branch first.

2. Market entry — should we enter?: A European logistics firm is considering expanding into the UK parcel market. What do you assess?

Four lenses: (1) market attractiveness (size, growth rate, margin profile), (2) competitive intensity (incumbents, switching costs, pricing), (3) client capabilities (existing routes, relationships, regulatory knowledge), (4) entry economics (capital required, payback period, IRR). Land on a clear recommendation with the dominant risk.

3. Market sizing: Estimate the number of weekly grocery deliveries made in London.

Population of London (~9m). Average household size (~2.4), so ~3.75m households. Estimate penetration of grocery delivery (~30% use it at least weekly) = ~1.1m deliveries per week. Sense check: ~13% of UK grocery spend is online (ONS retail data), London skews higher. Rough order of magnitude looks plausible.

4. Growth — which lever?: A SaaS company wants to grow revenue 20% next year. It currently earns revenue from 1,000 enterprise clients at an average contract value of £50,000. What are its options?

Three levers: (1) acquire new clients (volume), (2) raise average contract value (price), (3) expand existing clients (cross-sell or upsell). Quantify each: 200 new clients at £50k = £10m; 5% price rise on existing = £2.5m; 10% upsell to 500 clients = £2.5m. Recommend based on feasibility and margin impact.

5. PEI — Drive: Tell me about a time you pursued an ambitious goal in particularly tough circumstances.

Structure: Situation (context, why it was hard), Role (what specifically you were responsible for), Actions (the three or four concrete steps you took, not the team), Obstacles (what got in the way and how you specifically handled it), Outcome (quantified where possible), Reflection (what you would do differently). Keep the opening to two minutes. Wait for follow-ups.

6. Profitability — drill down: The COGS increase is entirely in raw material costs. What do you do next?

Ask whether the increase is in price per unit or volume consumed. If price: is it market-wide (commodity inflation) or supplier-specific? If volume: is product yield falling, or is waste increasing? Each branch leads to a different recommendation (renegotiate contracts, hedge commodity exposure, fix production line, review recipe). Show you are driving the tree, not just naming buckets.

7. M&A — should we acquire?: A media company is considering acquiring a podcast network for £200m. How do you evaluate it?

Three lenses: (1) strategic fit (does it fill a content gap or bring an audience the acquirer lacks?), (2) financial return (what are the synergies, what multiple does £200m represent, what is the payback period?), (3) integration risk (culture, technology, talent retention). Ask for the revenue and EBITDA of the target before modelling.

8. Estimation — sense check: How many espresso shots are consumed in London coffee shops each day?

London population ~9m. Assume ~60% are adults who drink coffee, ~40% of those visit a coffee shop on a given day = ~2.2m coffee shop visits per day. Assume ~70% order espresso-based drinks, average ~1.3 shots per drink = ~2m shots. Round to ~2m per day as a working estimate.

9. BCG Casey — exhibit question: You are shown a chart: a company’s gross margin has been flat at 40% for three years while net margin has fallen from 12% to 6%. What does this tell you?

The problem is below the gross margin line. Fixed operating costs, SG&A, D&A or interest expense have increased relative to revenue. The gross margin stability tells you product economics are intact. Drill into which below-the-line cost has grown fastest in the period.

10. PEI — Growth: Tell me about a time you received critical feedback and changed your approach as a result.

The trap is choosing a humblebrag. The strongest answer: a genuine failure, a specific piece of feedback from a specific person, the exact behavioural change you made, and a concrete example of the new approach working. The interviewer will probe: What exactly did they say? What did you think when you heard it? What specifically did you do differently? Have the detail ready.

How to use Merra to prepare

Merra’s McKinsey Associate Case practice tile runs you through a full AI-led case in the McKinsey interviewer-led format. The AI asks clarifying questions, provides exhibit data on request, and presses you when your answer is vague. Unlike a static practice case, the AI talks back — so you get the same kind of real-time pressure you will face in the room.

Other Merra tiles relevant to consulting prep:

• Deloitte Graduate Consultant — structured competency interview practice

• PwC Audit Associate — professional services fit question practice

• KPMG Grad Scheme Strengths — strength-based interview format

You can practice live at trymerra.ai/practice. Interview and Coach modes are free. Additional modes including Beast, Hype, Curveball, Rapid Fire, Skeptic, Silent Treatment and Devil’s Advocate are available on Pro.

6-week MBB case interview prep plan

Weeks 1-2: Foundations

Learn the core frameworks (profitability, market entry, growth, M&A). Do one timed case per day on your own. Practise mental arithmetic drills daily — percentage calculations, estimation, ratios. Run Merra’s McKinsey case tile at the end of each week to stress-test your structure.

Weeks 3-4: Case volume

Practise two to three cases per week with a partner. Video yourself once per week and review your recommendation delivery. Build your PEI stories for all four McKinsey dimensions. Start timing your Casey-style solo cases.

Weeks 5-6: Simulation

Run full timed mock interviews. Simulate the online assessments under test conditions. Refine your weakest case type. Polish your 90-second firm-specific pitches for BCG and Bain fit rounds.

Most competitive candidates complete 50-80 cases across the full prep period. Quality of reflection after each case matters more than raw volume.

About the founder

Ahmed Ghelle is the founder of Merra. Merra builds voice-based AI mock interviews that talk back, helping students prepare for consulting, banking, and graduate scheme interviews. He writes about hiring, interview preparation, and the gap between how people practise and what actually works.