A rate "lock" or "commitment" is a lender's promise to lock in a specific interest rate and a certain number of points for you for a certain period during your application process. This prevents you from working through your whole application process and finding out 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 spans usually costing more. You can get a longer period for your lock, but in making this choice, will likely have a higher interest rate than you would have with a shorter rate lock period
In addition to going with a shorter rate lock period, there are other ways you can attain the lowest rate. A larger down payment will give you a better interest rate, because you'll be starting out with a good deal of equity. You could opt to pay points to lower your interest 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 life of the loan. You pay more up front, but you will save money, especially if you don't refinance early.
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