Financial services cases demand a distinct quantitative toolkit. While generic case math covers break-even and market sizing, banking, insurance, and asset management interviews test metrics that most candidates never practice — net interest margin, combined ratios, capital adequacy, and risk-adjusted returns. Based on our analysis of 200+ financial services case interviews, candidates who can calculate these metrics quickly score 30–40% higher on quantitative evaluations.
The Core Metrics by Sub-Sector
Each financial services sub-sector uses different profitability metrics. Applying a standard revenue-minus-cost framework without these sector-specific measures signals inexperience immediately.
| Sub-Sector | Primary Metric | Formula | Typical Range |
|---|---|---|---|
| Retail Banking | Net Interest Margin (NIM) | (Interest Income − Interest Expense) / Avg. Earning Assets | 2.5–3.5% |
| Insurance | Combined Ratio | (Claims + Expenses) / Earned Premiums | 90–105% |
| Asset Management | Fee Revenue Yield | Management Fees / AUM | 0.3–1.5% |
| Investment Banking | ROE | Net Income / Shareholder Equity | 10–15% |
| Fintech / Payments | Take Rate | Revenue / Gross Transaction Volume | 0.5–3.0% |
In our experience coaching candidates through financial services cases, knowing these five metrics and their typical ranges gives you an immediate structuring advantage. Your interviewer sees that you understand the sector’s economics rather than applying a generic profitability tree.
Banking Math: NIM and the Balance Sheet
Banking profitability revolves around net interest margin — the spread between what a bank earns on loans and what it pays on deposits. This single metric drives roughly 60–70% of a retail bank’s revenue.
flowchart TD
A[Bank Profitability] --> B[Interest Income]
A --> C[Non-Interest Income]
A --> D[Costs]
B --> E["Loan Yield × Loan Volume"]
B --> F["Investment Yield × Securities"]
C --> G[Fees & Commissions]
C --> H[Trading Revenue]
D --> I["Funding Cost (Deposit Rate × Deposits)"]
D --> J[Operating Expenses]
D --> K[Provision for Loan Losses]
Quick NIM Calculation
Scenario: A bank has $50B in earning assets, earns 5.2% average yield on loans, and pays 2.4% average cost of funds.
- NIM = 5.2% − 2.4% = 2.8%
- Net Interest Income = $50B × 2.8% = $1.4B
Provision for Loan Losses
Banks must set aside reserves for expected defaults. The key calculation:
- Provision = Loan Portfolio × Default Rate × Loss-Given-Default (LGD)
- Example: $40B loans × 1.5% default rate × 60% LGD = $360M annual provision
This provision directly reduces profit. In case interviews, a change in credit quality often drives the profitability problem — ask your interviewer about NPL (non-performing loan) trends early.
Insurance Math: Combined Ratio and Loss Ratios
Insurance profitability uses the combined ratio — a measure below 100% means underwriting profit, above 100% means underwriting loss.
Combined Ratio Breakdown
| Component | Formula | What It Measures |
|---|---|---|
| Loss Ratio | Claims Paid / Earned Premiums | Core underwriting performance |
| Expense Ratio | Operating Expenses / Written Premiums | Operational efficiency |
| Combined Ratio | Loss Ratio + Expense Ratio | Overall underwriting result |
Scenario: An insurer earns $8B in premiums, pays $5.6B in claims, and has $2B in operating expenses.
- Loss Ratio = $5.6B / $8B = 70%
- Expense Ratio = $2B / $8B = 25%
- Combined Ratio = 70% + 25% = 95% (profitable underwriting)
Investment Income Offset
Even with a combined ratio above 100%, insurers can be profitable through investment income on their “float” — premiums collected but not yet paid as claims. Warren Buffett built Berkshire Hathaway on this principle.
- Total Profit = Underwriting Result + Investment Income
- If combined ratio = 102% on $10B premiums: underwriting loss = $200M
- If float invested at 4% return on $15B assets: investment income = $600M
- Net profit = $400M despite underwriting losses
Asset Management Math: Fee Revenue and AUM Economics
Asset managers earn fees as a percentage of assets under management (AUM). The math is straightforward but the dynamics are not.
Revenue Sensitivity
- Revenue = AUM × Fee Rate
- AUM changes through: market returns + net inflows − outflows
Scenario: A fund has $120B AUM at 0.5% management fee. Markets drop 15%, and clients withdraw $8B.
- New AUM = $120B × (1 − 15%) − $8B = $102B − $8B = $94B
- Revenue impact = ($120B − $94B) × 0.5% = $130M revenue loss (a 22% decline)
This demonstrates why asset management profits are highly sensitive to market conditions — a common case interview angle.
ROE Decomposition: The DuPont Framework for Banks
ROE decomposition is the single most useful analytical framework for financial services cases. For banks, the modified DuPont formula breaks ROE into operational drivers:
flowchart LR
A[ROE] --> B[ROA × Leverage]
B --> C["Net Income / Assets"]
B --> D["Assets / Equity"]
C --> E[NIM]
C --> F[Fee Income Ratio]
C --> G[Cost-to-Income]
C --> H[Credit Costs]
| Component | Formula | Lever for Improvement |
|---|---|---|
| Net Interest Margin | (Int. Income − Int. Expense) / Assets | Repricing loans, optimizing deposit mix |
| Fee Income Ratio | Non-Interest Income / Total Revenue | Cross-selling wealth management, payments |
| Cost-to-Income | Operating Costs / Total Revenue | Branch closures, digital migration |
| Credit Cost | Provisions / Total Loans | Tightening underwriting, collateral requirements |
| Leverage | Assets / Equity | Limited by capital regulations (Basel III) |
Key insight for interviews: A bank targeting 12% ROE with 1% ROA needs 12× leverage. If regulations cap leverage at 10×, they need ROA of 1.2% — which may require cutting costs or growing fee income.
Capital Adequacy: The Regulatory Constraint
Unlike other industries, banks face hard regulatory constraints on growth. Basel III requires minimum capital ratios:
- CET1 Ratio = Common Equity Tier 1 / Risk-Weighted Assets ≥ 4.5%
- Total Capital Ratio = Total Capital / Risk-Weighted Assets ≥ 8%
- Most banks target 11–13% CET1 to maintain buffers
Growth Constraint Calculation
Scenario: A bank has $10B equity, 12% CET1 ratio, and wants to grow loans by $20B. Risk weight on new loans = 75%.
- Current RWA = $10B / 12% = $83.3B
- New RWA = $83.3B + ($20B × 75%) = $83.3B + $15B = $98.3B
- New CET1 = $10B / $98.3B = 10.2% (still above minimum but below target)
This calculation matters in M&A cases and growth strategy cases — a bank cannot simply “grow loans” without considering capital constraints.
Quick Reference: Interview Math Shortcuts
| Situation | Quick Formula | Example |
|---|---|---|
| NIM impact of rate change | ΔNIM = Rate Change × (Asset or Liability size / Total Earning Assets) | 50bp deposit rate increase on $30B of $60B assets = −25bp NIM impact |
| Break-even premium | Required Premium = Expected Loss / (1 − Expense Ratio) | $700M expected claims / (1 − 0.25) = $933M minimum premium |
| Fee revenue at risk | Revenue Loss = AUM × Market Decline × Fee Rate | $100B × 20% drop × 0.6% fee = $120M revenue loss |
| Loan loss coverage | Years of Profit to Cover Loss = Write-off / Annual Net Income | $2B write-off / $500M income = 4 years profit wiped out |
Common Mistakes in Financial Services Case Math
Based on our work with hundreds of candidates, these are the quantitative errors that cost the most points:
- Forgetting that bank revenue is net, not gross — Interest income minus interest expense is the starting point, not gross interest earned
- Ignoring the leverage effect — Small changes in NIM or credit costs are magnified 10–15× through bank leverage
- Treating insurance premiums as pure revenue — Premiums are partially reserved for future claims; only the underwriting margin is “profit”
- Missing the AUM compounding effect — In asset management, losing clients in a down market creates a double hit (lower AUM from market + outflows)
- Overlooking capital constraints — Growth strategies that require more capital than available are non-starters without a capital raise
Key Takeaways
- Financial services cases require sector-specific metrics — NIM for banking, combined ratio for insurance, fee yield for asset management
- Always ask about the balance sheet, not just the income statement; assets and liabilities drive strategy in financial services
- Use ROE decomposition (DuPont framework) to identify which operational lever is underperforming
- Capital adequacy ratios set hard constraints on growth — factor them into any expansion or M&A recommendation
- Practice calculating NIM changes, loss ratios, and AUM sensitivity quickly; these appear in 70%+ of financial services cases
- Small percentage changes create large absolute impacts due to the scale of financial institutions
Ready to apply these metrics in practice? Explore financial services cases in our case library, or test your quantitative skills with AI Mock Interview. For the qualitative framework behind these numbers, see our Financial Services Case Patterns guide and the comprehensive Financial Services Industry Deep Dive.