US wealth inequality and long-term real interest rates exhibit a strong negative correlation over the post-war period.We quantify how much of the observed increase in wealth inequality from 1983 to 2023 can be accounted for by the decline in rates. To do so, we combine asset holdings data with asset exposures to interest rates to measure the exposure of households’ portfolios to interest rates. The portfolios of the wealthy have higher interest rate exposure due to a tilt toward equity-like assets with long duration. As a result, wealth inequality increases when rates fall. When we feed in the observed path of real interest rates, we find that this revaluation effect explains the majority of the increase in measured wealth inequality over the past forty years.