A rate "lock" or "commitment" is a lender's promise to set a particular interest rate and a certain number of points for you for a specified period during your application process. This protects 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 15 to 60 days, with the longer ones generally costing more. A lending institution may agree to lock in an interest rate and points for a longer period, say sixty days, but in exchange, the rate (and sometimes points) will be higher than with a rate lock of fewer days.
There are other ways to get a reduced rate, in addition to choosing a shorter rate lock period. The larger down payment you pay, the lower the rate will be, because you will have more equity from the start. You could opt to pay points to lower your rate over the loan term, meaning you pay more up front. To a lot of people, this makes financial sense..
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