When the Federal Reserve begins cutting the federal funds rate, the financial sector moves on two contradictory tracks at once. One line goes up — bond prices, which rally as yields fall, lifting the value of fixed-income portfolios. The other line goes down — net interest margins (NIM), the spread between what banks earn on loans and what they pay depositors. For firms like Bank of America and Charles Schwab, those two lines are pulling hard in opposite directions, and where you sit on the balance sheet determines everything.
The mechanism is straightforward. Banks fund themselves with short-term deposits and lend or invest at longer durations. When the Fed cuts short rates, deposit costs eventually fall — but banks also locked in assets at higher yields. The problem: the repricing is asymmetric. Loan books and held-to-maturity (HTM) bond portfolios don't immediately reprice higher just because rates drop. What they do is recover unrealized losses on the balance sheet, which is accounting relief, not cash. Meanwhile, the trading desk that marks its portfolio to market every day captures the bond rally in real time.