A rate "lock" or "commitment" is a promise from the lender to freeze a specific interest rate and a certain number of points for you for a certain period during your application process. This ensures that your interest rate will not get higher while you are going through the application process.
Although there might be a choice of rate lock periods (from 15 to 60 days), the extended spans are usually more expensive. You can get a longer period for your lock, but in doing so, will probably have a higher interest rate than you would have with a shorter period
In addition to going with a shorter lock period, there are more ways you may be able to attain the lowest rate. A larger down payment will give you a reduced interest rate, because you'll have more equity from the beginning. You can pay points to lower your rate over the loan term, meaning you pay more initially. One strategy that is a good option for many people is to pay points to improve the interest rate over the life of the loan. You'll pay more up front, but you'll come out ahead, especially if you don't refinance early.
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