A rate "lock" or "commitment" is a lender's promise to lock in a particular interest rate and a particular number of points for you for a certain period of time during your application process. This ensures that your interest rate will not grow as you are working through the application process.
While there can be a choice of rate lock periods (from 15 to 60 days), the extended ones are usually more expensive. A lending institution may agree to lock in an interest rate and points for a longer period, like sixty 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 good rate, besides choosing a shorter rate lock period. The larger down payment you make, the better the rate will be, because you will have more equity from the beginning. You could choose to pay points to improve your rate for the life of the loan, meaning you pay more initially. For many people, this makes sense and is a good deal..
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