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

A rate lock guarantees your interest rate for a specific window while your loan is processed, protecting you if rates rise before closing. Most lenders lock automatically once you are under contract, though the length of that window and any extension fees vary by lender. Skipping a lock leaves your rate floating, which can work in your favor if rates fall but against you if they climb. Ask your lender when their standard lock period starts relative to your closing date.