What is a rate lock, and what happens if my mortgage rate lock expires before closing?

A rate lock is the lender's promise to hold your quoted interest rate for a set period, commonly 30, 45, or 60 days, protecting you if market rates rise before closing. If your lock expires before you close, you may have to pay a lock-extension fee or, worse, accept whatever the current market rate is, which could raise your monthly payment. Locks usually start when your offer is accepted and the loan is in process. Ask about the cost of extensions upfront and whether a float-down option is available, which lets you capture a lower rate if the market drops during the lock. Push your lender and title company to close on schedule so the lock does not lapse.