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 consulting firms, 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 more finance-heavy end of the spectrum. Candidate reports and prep guides commonly describe math-heavy financial modeling and written-case components for some roles or rounds. Treat that as a prep signal rather than a universal promise: if you ignore FS-specific vocabulary going in, exhibits can become hard to interpret quickly.

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 know the formulas can spend their mental energy on interpretation; candidates who derive them live often lose time on each 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, ROE in the low-to-mid teens is often treated as healthy in a stable rate environment; lower figures require context on rates, capital levels, and business mix.

Net Interest Margin (NIM). NIM = (Interest Income − Interest Expense) / Average Earning Assets. Diversified retail banks often show higher NIM than corporate and investment banks because of balance-sheet mix (Source: FDIC, Bank Net Interest Margin working paper, 2005). NIM is rate-sensitive: when central bank rates rise, asset repricing can lead 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; figures in the mid-to-high 90s are often strong for commercial insurers. Combined ratio above 100% means the insurer loses money on underwriting and needs investment income or other offsets for profit.

Mental math reference table

The fastest way to make these formulas automatic is timed reps until the arithmetic stops costing you mental energy.

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 by shifting mix toward variable-rate commercial, which repriced faster; (2) defend deposits by growing non-interest-bearing checking to hold funding cost down; (3) rebalance to fee income, since Midland's non-interest-income share is 27%, below the 35-40% regional bank benchmark. Priority 1 and 3 could recover meaningful NIM and ROE over the next 12-18 months.

Reading a dense FS exhibit, pulling the driver, and explaining the movement under time pressure is its own skill. OW and Deloitte FS rounds lean heavily on it.

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%; that adds 70 bps and cuts break-even to year 2.

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 case math practice drills hit these directly, as do finance-heavy practice packets from established case-prep sources.

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 should add written case practice: synthesize a 3-5 slide recommendation from a multi-exhibit packet under time pressure.

Checklist

Finance case interview readiness checklist

• I can derive and compute NIM, ROE, CET1 ratio, and combined ratio without prompts

• I can read a bank income statement and segment revenue into NII and non-interest income

• I know the Basel III minimum CET1 ratio and conservation buffer (7.0% total)

• I have completed 10+ finance-specific cases, at least 4 Oliver Wyman candidate-led

• I can write a 3-slide recommendation from an 8-exhibit packet in under 45 minutes

• I know 15 core FS terms well enough to use them without asking for basic definitions

Sources

Sources checked June 17, 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