When you’re shopping for a new refinance mortgage, it’s important to find and secure the lowest interest rate possible. Getting a written mortgage lock-in is a sure way to protect the low rate you’ve worked hard to get.A mortgage rate lock-in, is a lender’s guarantee to hold an agreed upon interest rate and points for a specific period of time. When negotiating a refinance home loan, it’s wise to lock-in your mortgage rate long enough to take you through the closing process. Typical lock-ins range from 30 to 60 days in length, although longer periods are possible.Some lenders may charge you a fee for locking in your loan rate. The amount of the lock-in fee can be anywhere from zero to five hundred dollars and will vary from lender to lender. Fees also depend on the length of the lock-in you request. Always be sure to request a written lock-in instead of a verbal one so that you have a record of the lock-in agreement.If mortgage interest rates happen to go down during the lock-in period, many lenders will reduce the interest rate of your loan accordingly. Ask your lender whether they have a (float-down) policy. A float-down policy reduces your rate if mortgage interest rates go down during the lock-in period.When requesting a mortgage rate lock-in, make sure the time period you request is long enough to cover you all the way through to the closing of the loan. Ask your lender what their policy is in case of an unexpected delay in the closing of the loan. Extensions are possible, but some lenders charge an additional fee for extending the length of a lock-in.