Mortgage interest rates change on a daily basis and can vary wildly depending on how the market is moving. Though refinances take less time than getting your first loan, they still don’t close in a day. A rate lock allows you to lock in your interest rate and keep the same rate while your lender closes your loan. This can protect you against changes in market interest rates and keep your loan predictable.   Ask your lender if they offer rate locks. If they do, ask how long you can lock your rate for and if locks are free. You should also ask about the cost to extend your rate lock if your refinance takes longer than expected.