Net Interest Income Explained: Why NII Matters in Bank Results Like RBL and Can Fin

When a bank or lender reports results, net interest income is usually the first number analysts go to. If a headline says a bank’s “core income” rose, it almost always means NII. Here we have net interest income explained from the ground up: what it is, how it’s calculated, how it differs from net interest margin, what moves it, and how to read it in actual results. We’ll use two lenders that put out Q2 FY27 numbers on 12 October 2026, RBL Bank and Can Fin Homes.

Net interest income explained: the basic idea

Strip a bank down and the core business is simple. It borrows from depositors and other lenders, and lends that money out at a higher rate. What it earns on loans and investments, minus what it pays on deposits and borrowings, is its net interest income.

NII = Interest earned − Interest expended

• Interest earned covers interest on loans (advances), on investments such as government bonds, and on balances kept with the RBI and other banks.
• Interest expended covers interest paid on savings and fixed deposits, and on the borrowings and bonds the bank has issued.

Think of NII as a lender’s version of a manufacturer’s gross profit. It’s what the core activity leaves behind before operating costs, provisions and tax. Fees, commissions, treasury gains and the like are not part of it. Those get reported separately as “other income”.

A simple illustration

Illustrative example: take a small bank with ₹10,000 crore of loans earning an average 10% a year, and ₹10,000 crore of deposits costing an average 6%. In a year it earns ₹1,000 crore of interest and pays out ₹600 crore, so NII is ₹400 crore. Grow the loans to ₹12,000 crore at the same rates, funded by more deposits, and NII goes up to ₹480 crore. If instead deposit costs climb to 7% while loan yields stay at 10%, NII on the original book drops to ₹300 crore. Volume and spread. Those two levers explain nearly every change in NII.

NII grows in two ways: lend more, or earn a wider spread on what you lend. The best quarters do both; the worrying ones grow volume while the spread quietly shrinks.

NII vs NIM: why both matter

Net interest margin (NIM) shows NII as a percentage of the assets that earn interest:

NIM = NII ÷ Average interest-earning assets (usually annualised)

NII is a rupee figure, and it tends to go up as a lender gets bigger. NIM tells you how profitable each rupee of lending is. So a lender can post higher NII while its NIM slips, which means it’s growing by lending more at thinner margins. That’s exactly what happened at Can Fin Homes this quarter, as you’ll see below.

Reading NII in real results: two Q2 FY27 examples

RBL Bank: fast volume growth

RBL Bank’s NII rose 37.4% year on year to ₹2,131 crore in the September quarter, from ₹1,551 crore, CNBC-TV18 reported. The balance sheet shows where it came from. Net advances grew 42% to ₹1,42,314 crore and deposits grew 34% to ₹1,56,272 crore. Net profit jumped to ₹481.7 crore from ₹179 crore. Our RBL Bank Q2 results analysis has the full set of numbers.

The obvious next question for an analyst: loans are growing faster than deposits and the CASA ratio is 27.2%, so can the bank hold funding costs down and stop margins eroding as it grows?

Can Fin Homes: NII up, margin down

Can Fin Homes, a housing finance company, reported NII of ₹431 crore in Q2 FY27, up about 7% from ₹404 crore, The Economic Times reported. Its loan book grew 10% to ₹43,539 crore. Its NIM, though, fell to 3.89% from 4.02% a year earlier.

Read together, NII grew more slowly than the loan book because the spread got thinner. Profit still rose 10% to ₹275 crore, with help from other lines of the income statement, but the margin trend is what we’d keep an eye on. Our Can Fin Homes Q2 report goes into more detail.

What drives NII up or down

• Loan growth: lend more and you earn more interest, other things being equal.
• Loan mix: unsecured loans like credit cards and personal loans yield more than home loans or corporate loans, but they also carry more credit risk.
• Cost of funds: a bigger share of low-cost current and savings account (CASA) deposits keeps interest expense down. Banks leaning more on term deposits and borrowings pay more.
• Interest rate cycle: when the RBI hikes, loans tied to external benchmarks reprice fast, which often lifts NII in the short run while deposit costs catch up later. When rates come down, the opposite tends to happen. Our explainer on how the RBI repo rate affects the stock market covers this.
• Cash reserve requirements: money parked with the RBI as CRR earns nothing, so stricter reserve rules can shave a little off NII. See our report on the RBI’s daily CRR rule change.
• Asset quality: once a loan turns into an NPA, the interest on it stops being recognised, and interest income drops.
• One-offs: interest on tax refunds, or recoveries from loans already written off, can puff up NII in a single quarter.

NII at banks vs NBFCs and housing finance companies

Every lender uses the same NII formula. What differs is the funding behind it, and that changes how you should read the number.

• Banks can raise current and savings account deposits, some of the cheapest money around. A strong CASA franchise is one of the biggest built-in advantages a bank can have on NII.
• NBFCs and housing finance companies mostly fund themselves through bank loans, bonds, commercial paper and, in some cases, public deposits. Their funding usually costs more, so they need higher-yielding loans or leaner costs to earn a similar margin. Can Fin Homes, for instance, had a deposit portfolio of just ₹239 crore against a loan book of more than ₹43,000 crore, according to The Economic Times. Nearly all its funding, then, comes from elsewhere.
• Microfinance and unsecured lenders earn the fattest yields but also carry the heaviest credit costs. Their NII can look excellent right up to the point provisions start climbing.

So compare NII growth and NIM within the same group, private banks against private banks and housing financiers against housing financiers, not across the whole sector.

How to analyse NII in a results release

1. Compare year on year, not only quarter on quarter. Seasonal factors and the number of days in a quarter distort sequential comparisons.
2. Set NII growth against loan growth. If loans grow 20% but NII grows 10%, margins are getting squeezed.
3. Check NIM and where it’s heading. A NIM that falls for several quarters is a warning, even while NII keeps rising.
4. Look at cost of funds and CASA. Higher deposit costs often show up in NIM a quarter or two later.
5. Read NII next to provisions. Strong NII doesn’t count for much if bad-loan provisions are rising faster. RBL Bank’s provisions, for example, went up to ₹766.5 crore from ₹599.2 crore in the previous quarter.
6. Watch for one-offs. Management commentary and the notes to accounts usually point out unusual items.
7. Compare with peers. A NIM of 3.9% means one thing for a housing finance company, another for a large private bank and something else again for a microfinance lender.

For lenders, NII is the engine and provisions are the brakes. Profit is what’s left after both, so never read one without the other.

NII in the wider income statement

To see where NII fits, you can build up a bank’s profit in steps:

• NII (core interest income)
• + Other income (fees, commissions, treasury gains)
• = Total income (net)
• − Operating expenses (staff, branches, technology)
• = Operating profit (pre-provision operating profit)
• − Provisions for bad loans and other risks
• − Tax
• = Net profit

The cost-to-income ratio (operating expenses ÷ net total income) shows how efficiently a lender turns that income into operating profit. At Can Fin Homes it rose to 19.59% from 18.55%, per The Economic Times. Still low, but it’s moving the wrong way, and so is the margin.

Why NII matters for bank stocks

NII is the biggest and most dependable part of a lender’s earnings, so the market reacts sharply to it. Beat on NII and NIM and investors read it as core strength. A beat that comes only from lower provisions or treasury gains gets treated as lower quality. With HDFC Bank, ICICI Bank and other big lenders reporting this week, NII growth and margin trends will drive a lot of how bank stocks trade. Our preview of Q2 results this week for banks and IT has the line-up.

Bottom line

Net interest income is what a lender earns on its loans and investments minus what it pays on its deposits and borrowings. It tells you how big the core business is, while NIM tells you how profitable it is. When you read results, set NII growth against loan growth, follow the NIM trend, and always weigh NII against provisions. Our two Q2 examples show the contrast well. RBL Bank grew NII sharply on fast loan growth, while Can Fin Homes grew NII more slowly than its loan book as its margin narrowed. For a complete framework, see our pillar on how to analyse quarterly results of a company.

This article is for education only and is not investment advice.