Finance Case Interview: Structure, Math, and Worked Examples (2026)

A finance case interview is a case interview set inside a bank, insurance company, asset manager, or fintech, where the interviewer expects you to work the real P&L drivers — net interest margin, combined ratio, capital ratios, RoRWA — instead of applying a generic profitability framework. Oliver Wyman, McKinsey FIG, and Deloitte FS Strategy run most of these cases; cases skew quantitative, vocabulary-dense, and faster than MBB generalist cases.

From Road to Offer's Oliver Wyman and FIG-focused practice sessions, the top predictor of pass/fail isn't case structure — it's whether the candidate instinctively thinks in unit economics (NIM, RoA, capital ratios) instead of generic profitability frameworks. Candidates who open a bank profitability case with "revenue, costs, competitors, customers" consistently underperform candidates who open with "interest income minus interest expense, divided by earning assets."

Where Finance Cases Show Up: Oliver Wyman FS, McKinsey FIG, Deloitte FS Strategy

Finance cases concentrate at three types of firms: pure-play financial services consultancies (Oliver Wyman, where roughly 60% of work is in FS), the Financial Institutions Group practices at generalist firms (McKinsey FIG, BCG FIG, Bain FSG), and Big 4 FS Strategy teams (Deloitte FS Strategy, EY-Parthenon FS, PwC Strategy& FS).

Oliver Wyman is the extreme end of the spectrum. According to IGotAnOffer's Oliver Wyman guide, the firm's cases include math-heavy financial modeling, and the final round written case is a 45-60 minute packet analysis requiring a 3-5 slide deliverable (Source: IGotAnOffer, Oliver Wyman Case Interview guide, 2026). If you ignore FS-specific vocabulary going in, you will be lost by exhibit two.

The 4 Finance Case Types

Finance cases collapse into four recurring structures. Knowing which type you're in within the first 2 minutes of the case saves 5-10 minutes of framework spin.

1. Market entry for a financial product or region. A bank wants to enter Southeast Asian retail banking, or a fintech wants to launch in the UK. The case centers on regulatory access, customer acquisition economics, and capital requirements.

2. PE investment thesis. Bain, Oliver Wyman, and many BCG PE practice interviews include a "should our client buy this asset" case. Structure: sources of returns (multiple expansion vs EBITDA growth vs leverage), diligence red flags, and entry/exit multiple comparison.

3. Trading desk or product-line profitability. A universal bank's FICC desk is losing money; a regional's mortgage unit is margin-compressed. Work a driver tree: revenue (NII + fees + trading gains), costs (compensation + tech + credit), RoRWA, and fixed cost absorption.

4. Regulation impact. Basel III Endgame changes capital requirements for operational risk. The case moves through balance sheet optimization (shrink RWA), repricing (move cost to customers), and portfolio reshaping (exit capital-heavy businesses).

Finance-Specific Math: ROE, Net Interest Margin, Basel Capital Ratios

Four calculation families dominate finance cases. Candidates who pre-memorize the formulas spend their mental energy on interpretation; candidates who derive them live lose 2-3 minutes per exhibit.

Return on Equity (ROE) and DuPont decomposition. ROE = Net Income / Shareholders' Equity. DuPont splits this into profit margin x asset turnover x financial leverage, which maps onto the bank P&L cleanly (Source: Federal Reserve, Beyond ROE working paper, 2010). For banks, "good" ROE is 10-15% in a stable rate environment; anything under 8% signals structural underperformance.

Net Interest Margin (NIM). NIM = (Interest Income − Interest Expense) / Average Earning Assets. A healthy NIM for a diversified retail bank runs 3.0% to 4.0%; corporate and investment banks run 1.5-2.5% on larger balance sheets (Source: FDIC, Bank Net Interest Margin working paper, 2005). NIM is rate-sensitive — when central bank rates rise, asset repricing usually leads deposit repricing, temporarily expanding NIM.

Basel III capital ratios. Common Equity Tier 1 (CET1) ratio = CET1 capital / risk-weighted assets (RWA). The minimum is 4.5% + 2.5% capital conservation buffer = 7.0% effective floor, plus G-SIB surcharges for the largest banks (Source: Bank for International Settlements, Basel III framework). Basel III Endgame, phasing in from 2025-2028 in the US, raises RWA for operational risk and reshuffles credit risk weightings (Source: PwC, Basel III Endgame Our Take, 2026).

Insurance combined ratio. Combined Ratio = (Claims + Expenses) / Net Premiums Earned. Anything under 100% is an underwriting profit; 95-98% is target territory for commercial insurers. Combined ratio above 100% means the insurer loses money on underwriting and depends entirely on investment income for profit.

Mental math reference table

Worked Example 1: Regional Bank Profitability

Prompt: "Our client is Midland Bank, a US regional with $80B in assets. ROE has dropped from 13% to 8.5% over three years. Why, and what should they do?"

Step 1 — Set up the profit tree. Net Income = Net Interest Income + Non-Interest Income − Provisions − Operating Expense − Tax. ROE = Net Income / Equity.

Step 2 — Ask for the numbers. The interviewer hands you this exhibit:

Step 3 — Compute the driver ratios.

• NIM Y1 = 2.16 / 72.0 = 3.00%
• NIM Y3 = 1.52 / 76.0 = 2.00%
• NIM compression = -100 bps (the primary driver)
• ROE Y1 = 0.82 / 6.3 = 13.0% (matches stated)
• ROE Y3 = 0.28 / 3.3 = 8.5% (matches stated)

Step 4 — Interpret. NIM dropped 100 bps because deposit cost repriced (interest expense more than doubled) faster than asset yield. This matches the late-2022 through 2024 US rate cycle, when regional banks saw deposit beta accelerate. Provisioning also doubled, absorbing another ~$80M pre-tax.

Step 5 — Recommend. Three levers: (1) reprice loans — shift mix toward variable-rate commercial, which repriced faster; (2) defend deposits — grow non-interest-bearing checking to hold funding cost down; (3) rebalance to fee income — Midland's non-interest-income share is 27%, below the 35-40% regional bank benchmark. Priority 1 and 3 recover ~60 bps of NIM and 500 bps of ROE over 18 months.

Worked Example 2: Fintech Go-to-Market

Prompt: "A fintech lender wants to enter the UK SMB loan market. Should they, and at what price point?"

Step 1 — Market. UK SMB lending: ~£60B outstanding. Addressable sub-segment (£25K-£250K loans, underserved by high-street banks): ~£12B. Year-3 capture target of 2.5% = £300M new originations.

Step 2 — Unit economics per loan.

• Average loan: £75,000, 36-month term, 12% APR
• Cost of funds (securitization): 6.5% → Gross NIM: 5.5%
• Expected loss: 2.5%/yr; Servicing: 1.0% → Risk-adjusted NIM = 2.0%
• CAC: £600, amortized over 3-year term
• Contribution per loan year 1 = £75,000 x 2.0% − £200 = £1,300

Step 3 — Break-even. Fixed cost base (tech + risk + compliance + UK IFPR capital): £12M/year. Break-even ≈ £12M / £1,300 ≈ 9,250 active loans, or ~£700M cumulative originations. At 2.5% capture (£300M/yr), break-even lands in year 3.

Step 4 — Recommend. Enter, but hold price. Cutting rate from 12% to 10% to accelerate capture drops risk-adjusted NIM to zero and pushes break-even past year 5. Instead, invest £4M in underwriting AI to compress expected loss from 2.5% to 1.8% — adds 70 bps and cuts break-even to year 2.

Test Your Finance-Case Readiness

Test yourself

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Question 1 of 3

A regional bank's NIM drops from 3.2% to 2.4% on $50B of earning assets. How much pre-tax NII was lost?

• A$40M
• B$200M
• C$400M
• D$800M

How to Prep: A 4-Week Plan for Finance Cases

Week 1 — Build the vocabulary. Read 10-K sections for one bank (JPMorgan Chase), one insurer (Chubb), one asset manager (BlackRock), and one fintech (Wise). Build flashcards for 15 core terms: NIM, NII, CET1, RWA, RoA, RoE, RoRWA, loss ratio, expense ratio, combined ratio, AUM, AUM yield, efficiency ratio, cost of funds, deposit beta.

Week 2 — Drill the math. One 30-minute daily session on NIM sensitivity, ROE decomposition, capital ratio computation, and combined ratio scenarios. Road to Offer's math drills hit these directly, as do Oliver Wyman practice packets on PrepLounge and IGotAnOffer.

Week 3 — Run 10 full FS cases. Mix 4 Oliver Wyman candidate-led cases, 3 McKinsey FIG, 2 BCG FIG, 1 Bain FSG. If any NIM or ROE calculation was off by more than 5 bps, redo the exhibit.

Week 4 — Simulate the full round. Two 90-minute blocks per day (case + PEI). Oliver Wyman candidates add one 45-minute written case packet per day: synthesize a 3-5 slide recommendation from an 8-exhibit packet.

Checklist

Finance case interview readiness checklist

Sources

Sources checked April 12, 2026:

• IGotAnOffer, Oliver Wyman Case Interview: Ultimate Guide
• Hacking the Case Interview, Financial Services Case Interview: Complete Guide
• CaseCoach, How to Prepare for Financial Services Case Interviews
• PwC, Basel III Endgame: Complete Regulatory Capital Overhaul
• Bank for International Settlements, Basel III capital framework
• FDIC, Sensitivity of Bank Net Interest Margins and Profitability
• European Central Bank, Beyond ROE: How to Measure Bank Performance
• IGotAnOffer, Case interviews: finance concepts you need to know
• Road to Offer, Oliver Wyman Case Interview Guide
• Road to Offer, Case Interview Math Practice

Related Guides

• Case Interview Frameworks: Complete Guide
• Case Interview Math: Mental Shortcuts
• Case Interview Math Practice Drills
• Oliver Wyman Case Interview Guide
• Break-Even Analysis for Case Interviews