What Is Net Interest Margin?

Net interest margin (NIM) is the fundamental measure of a bank's core business profitability. Banks make money primarily by borrowing at low rates (through deposits) and lending at higher rates (through loans). NIM captures this spread as a percentage of the bank's interest-earning assets.

A NIM of 3-4% is typical for US community banks. Large banks often have narrower margins (2-3%) because they rely more heavily on wholesale funding and compete aggressively for deposits. When interest rates rise, NIM dynamics depend on the bank's asset-liability mix. Banks with floating-rate loans and fixed-rate deposits see margins expand. Banks with fixed-rate loan portfolios and rate-sensitive deposits may see margins compress.

The interest rate environment from 2022-2024 created significant NIM pressure for many banks. As the Federal Reserve raised rates rapidly, the cost of deposits increased faster than the yields on existing loan portfolios for many institutions. This "margin squeeze" was particularly acute for banks that had loaded up on low-yielding, long-duration bonds during the low-rate era — exactly the situation that contributed to SVB's failure.

For depositors, NIM matters because it drives bank profitability, which in turn builds capital through retained earnings. A bank with a consistently strong NIM is generating the organic capital it needs to remain safe. On BankHealthData, NIM influences the ROA component of the Health Score indirectly: banks with healthy margins tend to show stronger ROA. If you are comparing banks, remember that NIM varies significantly by business model — do not expect a large money-center bank to match the NIM of a community bank.