# Reading a bank's income statement: net interest margin and the interest spread
A US regional bank and a large Eurozone bank both take deposits and make loans. Yet the US bank might earn roughly 3.3 cents of net interest income on every dollar of earning assets, while the European bank earns closer to 1.3 cents. Same business, more than double the margin. This lesson shows you how to calculate that number and why the gap exists.
Net interest margin (NIM) is the core profitability metric of traditional banking. It answers one question: how much does a bank earn from lending money, after paying for the money it borrows, relative to the assets that generate that income?
The formula:
NIM = Net Interest Income / Average Earning Assets
where:
Net Interest Income = Interest Income - Interest ExpenseTwo terms to define first:
Earning assets are the assets that actually generate interest: loans, leases, and investment securities. Cash sitting in a vault and the bank's headquarters building do not count. We use the *average* over the period (usually beginning plus ending balance, divided by two) because the asset base moves during the year.
Take a simplified regional bank. These figures are illustrative, not a real bank's filing:
Step 1, net interest income:
4,200 - 1,400 = 2,800Step 2, divide by average earning assets:
2,800 / 85,000 = 0.0329 = 3.29%So this bank runs a NIM of about 3.3%. That is a healthy, typical level for a US regional bank as of the mid-2020s.
You can pull the exact inputs from any bank's quarterly filing. US banks file the 10-Q (quarterly) and 10-K (annual) with the SEC, and most publish a supplemental "financial data" pack that states NIM directly. The SEC's EDGAR database is free and holds every US filing.
People use "spread" and "margin" loosely. They are not the same.
Interest rate spread is the difference between the average rate earned on assets and the average rate paid on liabilities:
Spread = (Interest Income / Earning Assets) - (Interest Expense / Interest-bearing Liabilities)NIM divides net interest income by earning assets only. The difference matters because banks fund some assets with money that costs nothing: non-interest-bearing deposits (a checking account paying 0%). Those free funds lift NIM above the spread. A bank flush with cheap current accounts will show a NIM noticeably higher than its raw spread. That gap is the value of the deposit franchise.
Rule of thumb: NIM is almost always higher than the spread, and the size of the gap tells you how good the bank's cheap funding is.
Now the comparison in the hook. As of 2024 to 2025, US banks broadly reported NIMs in the low-to-mid 3% range, while large Eurozone banks clustered closer to 1% to 1.5%. (These are approximate ranges from bank disclosures and supervisory data, not fixed figures; individual banks vary widely.)
Three structural drivers explain most of the gap.
US banks lend heavily into higher-yielding consumer products: credit cards, auto loans, and home equity lines. Yields on those are far above corporate lending. Many large Eurozone universal banks tilt toward lower-margin corporate loans, mortgages, and holding sovereign bonds, all of which yield less.
The typical US mortgage is a 30-year fixed-rate loan, often sold off but frequently held. In much of the Eurozone, mortgages are variable-rate or track a benchmark, and competition compresses the margin banks keep. Fixed-rate lending lets US banks lock in a wider spread when rates rise.
This is where the hook lands. US banks fund a large share of assets with low-cost or zero-cost deposits, especially retail checking. A meaningful chunk pays little or no interest. That is cheap raw material.
Eurozone banks endured years of negative policy rates (the European Central Bank's deposit rate was below zero from 2014 to 2022), which trained the market to expect thin margins and made it hard to charge borrowers much while paying depositors anything. Their funding also leans more on wholesale markets and interest-bearing deposits, which cost more than a free checking account.
> 🎬 [VIDEO: "Net Interest Margin Explained" - https://www.youtube.com/watch?v=n6cWyLbHFsU - a short, clear walkthrough of NIM mechanics and why it drives bank earnings]
| Feature | US regional bank | Eurozone universal bank |
|---|---|---|
| Typical NIM (approx, 2024-25) | ~3.3% | ~1.3% |
| Dominant loan yield | Higher (cards, autos) | Lower (mortgages, corporate) |
| Mortgage type | Often 30-year fixed | Often variable/tracker |
| Funding | Heavy cheap retail deposits | More wholesale + paid deposits |
| Rate environment legacy | Positive rates | Years of negative rates |
The lesson: NIM is not a scoreboard of management skill alone. It reflects the country's rate history, deposit habits, and product mix. A 1.3% European NIM is not "bad management." It is a different playing field.
Vérification des acquis
1. Why does net interest margin divide net interest income by average earning assets rather than by total assets?
2. A bank reports strong interest income but its NIM is low. Which explanation is most consistent with this?
3. Two banks run the identical lending business, yet one reports roughly double the NIM of the other. What does this most directly illustrate?
4. Select ALL correct answers about what counts as earning assets when computing NIM.
Sélectionnez toutes les réponses correctes.
5. Select ALL correct answers about the components of net interest income.
Sélectionnez toutes les réponses correctes.
A single NIM figure tells you little. Read it three ways.
NIM rises when rates rise faster on assets than on funding, and it compresses when depositors demand higher rates (called deposit beta: the share of a rate rise that a bank must pass on to depositors). In 2022 to 2023, US bank NIMs expanded as the Fed hiked. By 2024 to 2025, many compressed as deposit competition forced banks to pay up. Always ask: which direction, and why?
Compare a US regional only to other US regionals, and a Eurozone bank only to Eurozone peers. Comparing across the Atlantic tells you about geography, not performance.
A high NIM funds the bank's operating costs and credit losses. A bank with a 3.5% NIM but heavy loan losses may be worse off than a 1.5% NIM bank with pristine credit. NIM is the top of the funnelfunnelThe customer journey from awareness to purchase, typically Awareness, Interest, Consideration, Decision, Action, with prospects narrowing at each stage.Voir la définition complète →, not the bottom line.
For supervisory benchmarks across European banks, the European Banking Authority's Risk Dashboard publishes free aggregate NIM and profitability data by region.
A bank with a thin NIM can still be highly profitable if it earns large non-interest income: fees from asset management, payments, advisory, and trading. Many large Eurozone universal banks lean on exactly this. So a low NIM does not automatically mean low profit. Always pair NIM with the bank's fee income and its cost-to-income ratio (operating costs divided by total income) to see the full picture.