What is a mortgage rate lock and do I need one in 2026?

A mortgage rate lock is a lender's guarantee to hold a specific interest rate for a set period while a loan moves through underwriting, protecting a borrower from rates rising before closing. Most buyers do want one, since it removes the risk of the rate changing between application and closing, though it typically carries an expiration tied to the expected closing date. A rate lock does not protect against rates falling, so some lenders offer a one-time float-down option for an additional cost. A lender can explain the specific lock terms available before a buyer commits.