A rate "lock" or "commitment" is a lender's promise to freeze a certain interest rate and a specific number of points for you for a certain period while your application is processed. This keeps you from working through your entire application process and finding out at the end that the interest rate has risen higher.
Rate lock periods can be various lengths of time, anywhere from fifteen to sixty days, with the longer period usually costing more. You can get a longer period for your lock, but in doing so, will probably have a higher interest rate than you would with a shorter rate lock period
In addition to opting for a shorter rate lock period, there are more ways you can score the lowest rate. The larger down payment you can pay, the lower your interest rate will be, since you will have more equity from the start. You can pay points to bring down your rate for the term of the loan, meaning you pay more up front. One strategy that makes financial sense for some is to pay points to bring the rate down over the term of the loan. You'll pay more initially, but you'll save money, especially if you don't refinance early.
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