Net interest income tells you more than a bank's profit

What is net interest income, in plain terms?

A bank takes deposits and pays interest on them, then lends the money out at a higher rate. Net interest income is the gap, added up over a quarter, in rupees.

Take a made-up bank to see the mechanics. It holds ₹100 crore of deposits and pays 5 percent a year on them, which is ₹5 crore. It lends the same ₹100 crore at 9 percent, which earns ₹9 crore. Net interest income is ₹9 crore minus ₹5 crore, so ₹4 crore a year. Divide by the ₹100 crore the bank lends and you get a net interest margin of 4 percent.

Both numbers matter. NII in rupees grows when the bank lends more. The margin shows whether each rupee lent is earning more or less than before. A bank can post a higher NII and a thinner margin in the same quarter, because the balance sheet grew faster than the spread.

What did three banks report for the September 2026 quarter?

The three banks below reported on 17 and 18 October 2026, for the quarter ended 30 September 2026. Every figure is from Business Standard's report of the result, read on 19 October 2026.

• HDFC Bank: NII rose 9.7 percent to ₹34,620 crore and net profit rose 4.7 percent to ₹19,510 crore. Net interest margin was 3.16 percent of total assets.
• Axis Bank: NII rose 12 percent to ₹15,371 crore and net profit rose 38 percent to ₹7,003 crore. Net interest margin was 3.36 percent, against 3.73 percent a year earlier.
• IDBI Bank: NII rose 29 percent to ₹4,228 crore and net profit fell 39 percent to ₹2,205 crore. Net interest margin was 4.11 percent, against 3.71 percent a year earlier.

Source: Business Standard, HDFC Bank Q2FY27 result, Axis Bank Q2FY27 result and IDBI Bank Q2FY27 result, all read 19 October 2026.

Set the three lines side by side and the two columns disagree. IDBI Bank had the fastest-growing lending income of the three and the only fall in profit. Axis Bank's NII growth was in the middle and its profit growth was the highest. The ordering of profit growth is nearly the reverse of the ordering of NII growth.

Why does profit move differently from NII?

Profit is NII plus everything else a bank earns, minus what it spends and sets aside. Each of the other pieces can swing by more than the lending income does in a single quarter. The three reports show a different swing in each bank.

Mechanism 1: money set aside for bad loans

A provision is money a bank sets aside against loans that might not be repaid. It is charged against profit before the profit is counted. Business Standard reports that Axis Bank's provisions fell 52 percent in the quarter. NII grew 12 percent and provisions shrank by half, so profit rose 38 percent. Business Standard names the fall in provisions, beside NII growth, as what carried the profit. HDFC Bank's provisions and contingencies for the quarter were ₹3,570 crore, a credit cost ratio of 0.44 percent, and its profit grew more slowly than its NII.

Mechanism 2: gains from trading investments

Banks hold bonds and other investments, and selling them at a gain adds to income. HDFC Bank's treasury trading gains were ₹780 crore against ₹2,390 crore a year earlier, a fall of ₹1,610 crore. Business Standard reports that other income declined 3.6 percent, mainly on the fall in treasury gains. It adds that this, higher operating expenses and higher provisions partly offset the NII growth. Profit rose 4.7 percent against NII at 9.7 percent. Axis Bank's trading income fell from ₹498 crore to ₹85 crore in the same quarter.

Mechanism 3: a one-off sale

IDBI Bank's year-ago quarter included a one-off gain of ₹1,699 crore from selling its investment in NSDL. That year-ago profit was ₹3,627 crore. Take the gain out and the comparison base is ₹1,929 crore, so the ₹2,205 crore reported for the September 2026 quarter is a 14 percent rise. The headline said profit fell 39 percent. The business under it grew: NII rose 29 percent and margin rose from 3.71 percent to 4.11 percent. The fall came from a gain that will not repeat.

What is the case for reading NII before profit?

NII is the line that most directly records the thing a bank does for a living, which is lending against deposits. Profit gets pushed around by provisions, trading gains and one-offs, so one quarter of profit rarely tells you much about the next. A margin that moved from 3.73 percent to 3.36 percent says something about the cost of funds against the yield on loans.

My position: when a bank result arrives, read NII and margin first, then ask what else moved profit. If the answer is one line, such as a provision release or a stake sale, say so out loud before drawing any conclusion about the bank.

A worked check you can run on any result

Pick a quarter and a bank. Write down NII growth, profit growth and the gap between them in percentage points. For HDFC Bank it is 9.7 minus 4.7, so 5.0 points. For Axis Bank it is 12 minus 38, so minus 26 points. For IDBI Bank NII grew 29 percent and profit changed by minus 39 percent, a gap of 68 points.

A gap larger than a few points has a cause, and the report names it. Find the cause in the report before deciding what the quarter meant. A gap that comes from provisions is a different story from a gap that comes from a stake sale.

How does this carry over to an investing portfolio?

The habit is the same one a rule-based allocation is built on: decide by the underlying driver and set the headline aside. A position sized by rule does not need to guess whether last quarter's profit will repeat. Qatobit's QSI indices follow this idea for crypto. A published methodology fixes what each holding is for. A calendar-defined monthly rebalance then trims what has run hot and tops up what has lagged, as the methodology page describes (read 19 October 2026).

For a portfolio held on a schedule, the useful question after any result is which line made the headline and which line makes the business. Our pieces on how diversification is measured and on whether crypto belongs in a long-term portfolio apply the same reading to a whole allocation.

Frequently asked questions

What is the difference between net interest income and net interest margin?

Net interest income is the rupee gap between interest a bank earns and interest it pays. Net interest margin is that gap as a percentage of the assets or loans producing it. HDFC Bank's NII was ₹34,620 crore and its margin 3.16 percent of total assets in the September 2026 quarter.

Can a bank's profit fall while its net interest income rises?

Yes. IDBI Bank's NII rose 29 percent to ₹4,228 crore while its net profit fell 39 percent. The year-ago quarter held a ₹1,699 crore one-off gain from selling its NSDL investment.

Why did Axis Bank's profit grow faster than its net interest income?

Axis Bank's net interest income grew 12 percent while its profit grew 38 percent. Business Standard reports that provisions fell 52 percent in the quarter, alongside the NII growth.

Does a falling net interest margin mean a bank is doing badly?

Not by itself. Axis Bank's margin fell from 3.73 percent to 3.36 percent while its NII still grew 12 percent. The bank said FCNR-B deposits weighed on the margin, which was 3.47 percent without them.

Where can I read a bank's net interest income?

In the bank's quarterly results filing and in the press note released with it. Both give NII for the quarter and the year-ago quarter, with the margin beside it. Read the year-ago line too, because a one-off can sit in either.

Crypto investments are subject to market risk. Not financial advice.