A bank is not valued the way a factory or a software company is — and using the wrong method is the most common mistake investors make with financial stocks. This guide explains why the standard discounted cash flow breaks down on a bank, the ratios that actually decide a bank's worth, and how return on equity and price-to-book work together to set its fair value.
Why the usual method breaks down
For most companies, value comes from a discounted cash flow: you forecast the free cash the business throws off, discount it, and subtract net debt. That method rests on a clean line between the company's operations and its financing — the debt sits on one side, the business on the other.
For a bank, that line does not exist. Debt is the raw material of a bank's business, not a financing choice.
Think about what a bank actually does. It takes in deposits and borrowings — which are liabilities, a form of debt — and turns them into loans. The interest it pays on those deposits is its cost of goods sold. The interest it earns on loans is its revenue. So the concepts a normal DCF depends on — free cash flow, enterprise value, net debt — simply lose their meaning:
- Enterprise value is meaningless, because you cannot separate a bank from its debt. The debt is the enterprise.
- Free cash flow is impossible to define cleanly, because "cash" is the product the bank deals in, not a residual left over after operations.
A manufacturer's debt sits outside its operations. A bank's debt is its operations. That single fact is why a DCF cannot value a bank.
So banks need a different lens — one built around the return they earn on the only capital that truly belongs to shareholders: equity.
The right lens: return on equity against its cost
The heart of bank valuation is one comparison: the return on equity a bank earns, versus the cost of that equity.
Return on equity (ROE) is net profit divided by shareholders' equity — the profit the bank generates on owners' money. The cost of equity is the return shareholders require for the risk of owning it, typically around 12-14% for an Indian bank.
The rule that follows is simple and powerful:
- A bank earning ROE above its cost of equity is creating value, and deserves to trade above its book value.
- A bank earning ROE below its cost of equity is destroying value, and deserves to trade below book.
- A bank earning exactly its cost of equity is worth about 1x book value.
This is the excess-return (or residual-income) approach: a bank is worth its book value plus the value of all the returns it earns above the cost of its equity. It is the correct method for any lender, and it is the lens FairStocks uses on every Indian bank.
Turning ROE into a fair price-to-book
Because banks are valued off book value, the price-to-book ratio (P/B) is how their valuation is usually expressed. And ROE is what justifies it. A useful approximation for the fair multiple is:
\[\text{Justified P/B} \approx \frac{\text{ROE} - g}{K_e - g}\]
where $g$ is the sustainable growth rate and $K_e$ is the cost of equity. You do not need to solve this by hand — the point is the intuition it captures: the further a bank's ROE sits above its cost of equity, the higher the multiple of book value it is worth.
A rough feel for Indian banks:
- ROE ≈ cost of equity (~13%) → fair value near 1x book.
- ROE ~16-18%, sustained → fair value around 2-3x book — the territory of the best private banks.
- ROE in mid-single digits → fair value below 1x book — common for weaker public-sector lenders.
This is why a high-quality private bank and a struggling public-sector one can trade at wildly different multiples of book and both be fairly priced. The market is not being irrational — it is pricing very different levels of sustainable return.
Price-to-book on its own tells you almost nothing about a bank. Price-to-book read next to ROE tells you almost everything.
The ratios that decide the quality of the return
ROE tells you how much return a bank earns. Four more ratios tell you whether that return is durable or dangerous — because a bank can always lift its return for a while by taking on more risk.
- Net interest margin (NIM) — the spread between what the bank earns on loans and pays on deposits. It is the core engine of profitability. A stable, healthy NIM signals real pricing power.
- Gross and net NPAs — the share of loans that have gone bad. Asset quality is the single biggest risk in banking: a bank can look profitable for years and then surrender it all to a wave of defaults. Low and stable NPAs are non-negotiable for a quality bank.
- CASA ratio — the proportion of deposits sitting in low-cost current and savings accounts. A high CASA means cheap, sticky funding, which is a structural and lasting cost advantage.
- Capital adequacy (CAR) — the cushion of capital a bank holds against its loans. It measures resilience: how much loss the bank can absorb before it is in trouble.
A bank earning a high ROE on the back of a strong NIM, low NPAs, a high CASA and solid capital is earning it the right way. A bank earning the same ROE with thin capital, rising bad loans and expensive funding is borrowing that return from its future. The numbers can look identical for a year or two; the businesses are worlds apart.
Private versus public: reading the gap
The clearest illustration of all this is the gap between India's leading private banks and its public-sector lenders. Compare a bank like HDFC Bank or ICICI Bank against a public-sector peer, and the difference is not really about size — it is about sustainable ROE and asset quality.
A private bank compounding equity at 16-18% with low NPAs earns its two-to-three-times-book premium honestly. A public-sector bank earning a mid-single-digit ROE with a weaker loan book earns its near-book valuation just as honestly. Seeing the two side by side — on the same ROE, the same excess-return model, the same measures — is far more revealing than looking at either in isolation, because it strips the comparison down to the only things that matter for a bank: the return, and the risk behind it.
Check it for any bank
You do not need to build a residual-income model by hand. FairStocks values every listed Indian bank on the excess-return method — the lens that actually fits a lender — showing a decade of return on equity and the fair value that follows from it, so you can judge whether today's price-to-book is earned or borrowed.
The mistake to avoid is bringing a factory's toolkit to a bank. Forget enterprise value and free cash flow here. Ask instead the only question that values a lender: how much return does it earn on shareholders' equity, how safely, and for how long — and the fair price-to-book falls straight out of the answer.