A rate "lock" or "commitment" is a promise from the lender to freeze a specific interest rate and a specific number of points for you for a specified period of time during your application process. This saves you from working through your entire application process and discovering at the end that your interest rate has gone up.
Rate lock periods can vary in length, anywhere from fifteen to sixty days, with the longer ones generally costing more. You can get a longer period for your lock, but in doing so, will likely have a higher rate than you would have with a shorter rate lock period
There are more ways to get a low rate, besides agreeing to a shorter rate lock period. The larger the down payment, the lower your interest rate will be, since you will be starting with more equity. You may choose to pay points to bring down your rate for the loan term, meaning you pay more initially. One strategy that makes financial sense for some is to pay points to bring the rate down over the term of the loan. You are paying more up front, but you will come out ahead in the end.
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