Should I keep cash in a money market fund or a high-yield savings account?

Both are fine homes for cash, and they're close cousins — the right one depends on access and where the cash lives. A high-yield savings account (HYSA) is a bank product, FDIC-insured up to $250,000, with rates that move with the market and instant access. A money market fund is an investment held at a brokerage, not FDIC-insured (though very stable and often holding Treasuries), and convenient if your cash already sits with your broker. Yields are usually similar. A key wrinkle: government money market funds can hold Treasuries whose interest is exempt from state income tax, which helps high earners in high-tax states. For an emergency fund you'll touch often, an HYSA's simplicity wins; for idle brokerage cash, a money market fund earns more than a default sweep. Size your reserve at wealthserene.com/tools/emergency-fund.