Net interest margin is the gap between what a bank earns on its loans and investments and what it pays for its deposits and other funding, measured as a percentage of its interest-earning assets. It is the single clearest number for how profitable a bank's core lending business is. Across all US banks, the net interest margin was 3.32 percent in the second quarter of 2026, up one basis point from the prior quarter, according to the Federal Deposit Insurance Corporation's Quarterly Banking Profile released August 25, 2026.

What the number actually captures

A bank's basic job is to borrow cheaply and lend at a higher rate. It pays depositors some rate on checking, savings and certificates of deposit, and it earns a higher rate on mortgages, business loans, credit cards and the bonds it holds. The difference, scaled against the assets that earn interest, is the net interest margin.

If a bank earns 5.5 percent on its loans and securities and pays 2.2 percent on its funding, its net interest margin is roughly the 3.3 percentage points in between. That spread, multiplied across hundreds of billions of dollars of assets at a large bank, is where most traditional banks make most of their money. Our explainer on how banks make money sets out the full picture, but net interest margin is the heart of it.

Why it is only one basis point higher

The striking thing about the Q2 2026 figure is how little it moved: 3.32 percent, up just one basis point from 3.31 percent the quarter before. That near-flat reading captures a tug of war. When the Federal Reserve raises rates, banks can charge more on new loans, which helps the margin. But they also face pressure to pay more on deposits, because savers can move money to higher-yielding accounts, money-market funds or Treasury bills. When the Fed cuts, the reverse happens: loan yields drift down, and the margin depends on whether deposit costs fall as fast.

The gap between the policy rate and what banks actually pay depositors is sometimes called the deposit beta, and it is where a lot of bank profit is won or lost. A bank that can hold deposit costs down while loan yields hold up protects its margin; one that has to chase deposits with higher rates sees it squeezed. That is why a stable headline margin can hide very different results at individual banks.

Big banks versus small banks

The industry average hides a real split. Community banks, which rely more on plain lending and local deposits, reported a net interest margin of about 3.81 percent in the second quarter of 2026, well above the industry figure and up 19 basis points from a year earlier. The largest banks run lower margins because a bigger share of their balance sheet sits in lower-yielding securities and because they earn a large slice of their income from fees, trading and other non-interest sources that do not show up in the margin at all.

That is the catch with reading net interest margin on its own: for a diversified giant, it describes only part of the engine. For a traditional community bank, it describes almost the whole thing.

How it connects to what you earn and pay

Net interest margin is also a window into the rates you see as a customer. When margins are under pressure and banks are competing hard for deposits, savers tend to get better rates on high-yield savings accounts and CDs, because the banks need the funding. When banks are flush with cheap deposits and margins are comfortable, the rates offered to savers tend to be stingier. The margin and the rate on your savings account are two ends of the same spread. The policy rate set by the Federal Reserve feeds through to both sides, which is why the margin moves with the rate cycle.

Where it showed up this earnings season

Net interest margin was a recurring theme in the third quarter 2026 results from the big US banks, where management teams were quizzed on whether margins had bottomed as the Fed adjusted rates. The industry-wide figure from the FDIC, released with a lag, gives the aggregate backdrop; the individual bank results, which we covered in what to watch in Q3 2026 bank earnings, show how each institution managed the same squeeze differently.

How to read it

Do not read a single quarter's margin in isolation. Read the direction over several quarters, because a margin that is compressing tells you funding costs are rising faster than asset yields, and a margin that is expanding tells you the opposite. Compare a bank only against banks of a similar type, since community banks and money-center banks run structurally different margins. And remember what the number leaves out: for the biggest banks, fee and trading income can matter as much as the spread, so the margin is a vital gauge but never the whole story.

What to watch

Watch the trend in deposit costs, because that is the side of the margin most under a bank's control and most exposed to competition. Watch the gap between community-bank and large-bank margins, which signals where in the system the spread is healthiest. And watch what management says about the margin's direction, reported as their guidance rather than as a forecast, since it is the clearest tell of how they expect the next few quarters to run.