||The length of time a mortage lender will honor an agreed upon loan interest rate. Once a lender locks in your interest rate, that rate lock is good for a specific period of time. In order to finance your mortgage at the locked-in rate, you’ll need to close the loan within the rate-lock period. For example, if you have a 45-day lock-in period, you’ll need to close within 45 days of receiving the rate lock. Lenders usually charge a fee to lock in an interest rate, and the longer the lock-in period, the higher that fee will be.