A rate "lock" or "commitment" is a promise from the lender to set a specific interest rate and a specific number of points for you for a certain period of time while your application is processed. This saves you from going through your entire application process and learning 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 period generally costing more. You can get a longer period for your lock, but in doing so, will most likely have a higher rate than you would have with a shorter span of time
In addition to opting for a shorter lock period, there are more ways you can get the best rate. A larger down payment will result in a reduced interest rate, because you'll have more equity at the start. You can pay points to improve your rate for the term of the loan, meaning you pay more initially. For a lot of people, this makes financial sense..
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