A rate "lock" or "commitment" is a lender's promise to hold a specific interest rate and a certain number of points for you for a certain period during your application process. This saves you from going through your whole application process and discovering at the end that your interest rate has risen higher.
Rate lock periods can vary in length, between fifteen to sixty days, with the longer spans usually costing more. A lending institution can agree to hold an interest rate and points for a longer period, like 60 days, but in exchange, the rate (and sometimes points) will be more than that of a rate lock of fewer days.
There are other ways to get a better rate, in addition to opting for a shorter rate lock period. The more the down payment, the lower your interest rate will be, since you will be entering the loan with more equity. You can pay points to bring down 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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