A lock period is often 30 to 90 days, during which a mortgage lender is required to keep a specific loan offer access to a borrower. During this time, the borrower prepares for the loan closure while the lender processes the loan application. A mortgage rate lock is an agreement between a lender and a borrower that guarantees the borrower a fixed interest rate on the mortgage for the duration of the lock term, generally at the market interest rate. A loan lock protects the borrower from increased interest rates throughout the lock term.