We use transaction-level data from a major Icelandic bank—servicing about one third of the population—to study households’ portfolio allocation within liquid, short-term, safe assets—checking, savings, and brokered liquid funds—that are identical in risk, maturity, and liquidity but offer different yields. These assets are the main source of liquid financial wealth for households and the largest source of funding for banks. Despite instantaneous, costless transfers, most households barely respond to interest-rate spreads. We find that wealthy households are roughly ten times more responsive than the average, place larger shares in high-yield assets, and earn about two percentage points higher returns on their liquid portfolios than low-wealth households. Survey evidence suggests that financial literacy and inflation knowledge amplify responsiveness to interest rates. We show that business-cycle fluctuations in the share of low-rate deposits are driven primarily by active reallocation among wealthy depositors. Also, we find that standard portfolio-choice models with state- or time-dependent frictions, calibrated to match our estimated moments, are able to reproduce cross-sectional holdings but overstate households’ sensitivity to interest rates.