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 while your application is processed. This ensures that your interest rate won't get higher during the application process.
Rate lock periods can vary in length, between 15 to 60 days, with the longer period generally costing more. A lending institution will agree to freeze an interest rate and points for a longer span of time, such as sixty days, but in exchange, the rate (and sometimes points) will be higher than that of a rate lock of a shorter period.
There are more ways to get a reduced rate, besides agreeing to a shorter rate lock period. A larger down payment will give you a better interest rate, since you'll have a good amount of equity from the beginning. You may opt to pay points to lower your rate for the term of the loan, meaning you pay more up front. One strategy that is a good option for many people is to pay points to improve the rate over the term of the loan. You are paying more up front, but you will come out ahead, especially if you don't refinance early.
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