A rate "lock" or "commitment" is a lender's promise to lock in a particular interest rate and a specific number of points for you for a specified period of time during your application process. This ensures that your interest rate will not grow during the application process.
While there may be a choice of rate lock periods (from 15 to 60 days), the extended ones are generally more expensive. A lending institution can agree to freeze an interest rate and points for a longer span of time, say 60 days, but in exchange, the rate (and sometimes points) will be more than that of a rate lock of fewer days.
In addition to choosing a shorter rate lock period, there are several ways you can get the lowest rate. The bigger down payment you pay, the lower the interest rate will be, since you will be starting with more equity. You can pay points to lower your rate for the loan term, meaning you pay more up front. To many people, this makes financial sense..
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