What is a mortgage rate lock?

A rate lock is a lender's guarantee that you will receive a specific interest rate for a defined period — typically 30, 45, or 60 days. Once locked, your rate will not change even if market rates rise during that period. Rate locks are important because rates can fluctuate daily, and a small rate change can significantly impact your monthly payment. If closing is delayed beyond the lock period, you may pay an extension fee or be subject to a new rate. Some lenders offer float-down options that let you take advantage of a rate drop after locking, usually for an additional fee.