A bank's financial statements look wrong if you read them like a normal company's. Its “inventory” is loans, its raw material is deposits, its revenue is a spread rather than a sale, and it runs at leverage that would bankrupt an industrial firm — on purpose. So the usual toolkit misfires, and a handful of bank-specific ratios do the real work. Here are the five that tell you most, and what a healthy reading looks like.
1. Net interest margin — the engine
NIM = net interest income ÷ average interest-earning assets. This is the spread the bank lives on: what it earns on loans and securities minus what it pays for deposits and other funding, measured against the assets that actually earn interest. Most commercial banks run a NIM around 2–4%. Rising is generally good (wider spread), but read it with the environment — NIM often expands when rates rise and compresses when they fall, so a moving NIM can be the rate cycle, not the franchise.
2. Efficiency ratio — the cost discipline
Efficiency ratio = non-interest expense ÷ revenue. The one ratio where you want a small number: it's the cost to produce a dollar of revenue. Below ~55% is a lean, well-run bank; 55–65% is normal; north of 70% is a bloated cost base or a revenue problem. Track it over time — a creeping efficiency ratio is often the first sign a bank is losing operating discipline before it shows up in profit.
3. Loan-to-deposit — the funding balance
Loan-to-deposit = total loans ÷ total deposits. Deposits are a bank's cheapest funding; this ratio shows how much of them it has put to work as loans. Too high (above ~100%) and the bank is stretching its funding, leaning on costlier wholesale money and thinner liquidity; too low and it's leaving earnings on the table. Most healthy banks sit around 70–90%. In a stress scenario, a high loan-to-deposit ratio is one of the first things to worry about.
4. Provision rate — the credit signal
Provision for credit losses, against the loan book. This is the money a bank sets aside for loans it expects to sour, and it flows straight through to earnings. Watch the direction and the sign: a rising provision rate says management sees credit deteriorating; a negative provision is a reserve release (the bank now expects fewer losses — good for profit, but ask whether it's genuine or just flattering a quarter). Provisioning is where a bank tells you what it really thinks about the economy.
5. Return on assets — the honest scorecard
ROA = net income ÷ total assets. For most companies ROE is the headline, but for a bank — leveraged by design — ROE is inflated by that leverage and flatters weak franchises. ROA strips it out, so it's the cleaner read. About 1% ROA is the classic benchmark for a healthy bank; consistently above it is a strong operator, and near or below zero is a warning. (For why ROE and ROA diverge, see the ROE / ROA guide.)
Put them together
None of these means much alone; together they sketch the whole bank. A wide NIM, a low efficiency ratio, a sensible loan-to-deposit, stable provisions, and a ~1%+ ROA is a healthy, well-run institution. A compressing NIM, a creeping efficiency ratio, and a climbing provision rate — all at once — is a franchise under pressure, usually well before the headline profit admits it. And always glance at capital adequacy (the bank's equity cushion) in the filing: profitability means little if the balance sheet is thin.
Reading them in AnalystBook
For banks, AnalystBook computes the sector-right ratios — net interest margin, efficiency ratio, loan-to-deposit, provision rate, ROA/ROE — from the bank's own filings, and it's careful where the numbers are treacherous: NIM is only shown when there's enough earning-asset detail to compute it properly rather than a misleadingly high figure, and a provision's sign is preserved so a release doesn't read as a cost. Every ratio traces back to the filing line it came from, across the bank's history, so you can watch the five move together without rebuilding a bank model by hand. For research purposes only; not investment advice.