Net interest margin (NIM)
Net interest margin is the difference between the interest a lender earns and the interest it pays, shown as a percentage of its interest-earning assets.
NIM = (Interest earned − Interest paid) ÷ Average interest-earning assets × 100
What it is
A bank’s core business is simple: borrow money from depositors at one rate and lend it out at a higher rate. The gap between interest earned and interest paid is called net interest income.
NIM puts that gap in percentage terms, so you can compare banks of different sizes. A NIM of 3.5% means the bank earns ₹3.50 a year, after interest costs, on every ₹100 of loans and investments.
How to read it
A higher and stable NIM usually means the bank has cheap deposits (a good CASA ratio), lends to customers who pay higher rates, or both. A falling NIM means either its funding is getting costlier or its loans are earning less.
NIM differs a lot by lender type. Lenders focused on small personal or business loans usually earn higher NIMs than banks lending mostly to large companies, because the loans carry more risk.
Limits
A high NIM can come from lending to riskier borrowers. If those borrowers default, the extra margin disappears into bad loans. Always read NIM with the NPA trend.
NIM also ignores operating costs like branches and staff, and fee income. It describes the lending spread, not the whole bank.
Calculating NIM
A bank earns ₹8,000 crore of interest in a year and pays ₹4,800 crore of interest on deposits and borrowings. Net interest income is ₹3,200 crore. Its average interest-earning assets are ₹1,00,000 crore. NIM = ₹3,200 ÷ ₹1,00,000 × 100 = 3.2%.
Common mistakes
- Assuming a higher NIM always means a better bank, without checking loan quality.
- Comparing NIM between a microfinance lender and a corporate bank as if they were the same.
- Ignoring the direction of NIM over several quarters.
Interest earned is ₹600 crore, interest paid is ₹360 crore, and average earning assets are ₹8,000 crore. What is NIM?
- 3%
- 7.5%
- 4.5%
Show the answer
3%. Net interest income is ₹600 − ₹360 = ₹240 crore. ₹240 ÷ ₹8,000 × 100 = 3%.
Common questions
What is a good net interest margin?
It depends on the kind of lending. Compare a bank with similar lenders and its own past, and check that a high NIM is not coming with rising bad loans.
Why does NIM change when interest rates change?
Loan rates and deposit rates do not always reset at the same speed. Depending on which moves faster, a bank’s margin can widen or narrow for a while.
Is NIM the same as net interest income?
No. Net interest income is the rupee amount. NIM is that amount as a percentage of interest-earning assets.
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