A rate "lock" or "commitment" is a lender's promise to hold a certain interest rate and a particular number of points for you for a certain period of time while your application is processed. This prevents you from going through your whole application process and discovering at the end that the interest rate has gotten higher.
Rate lock periods can be various lengths of time, between 15 to 60 days, with the longer ones 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
There are more ways to get a reduced rate, besides agreeing to a shorter rate lock period. A bigger down payment will result in a better interest rate, because you're starting out with a good deal of equity. You might choose to pay points to bring down your interest rate for the loan term, meaning you pay more up front. For a lot of people, this is a good option..
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