A rate "lock" or "commitment" is a lender's promise to set 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 can't rise as you are working through the application process.
Although there might be a choice of rate lock periods (from 15 to 60 days), the longer ones are generally more expensive. You can get a longer period for your lock, but in doing so, will likely have a higher interest rate than you would have with a shorter period
There are more ways to get a low rate, in addition to going with a shorter rate lock period. A larger down payment will result in a reduced interest rate, because you'll have a good deal of equity at the start. You can pay points to reduce your rate over the term of the loan, meaning you pay more initially. To a lot of people, this makes financial sense..
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