A rate "lock" or "commitment" is a promise from the lender to hold a specific interest rate and a specific number of points for you for a specified period of time during your application process. This saves you from working through your entire application process and learning at the end that your interest rate has risen higher.
Although there are various lengths 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 rate lock period
There are more ways to get a low rate, besides choosing a shorter rate lock period. The bigger down payment you make, the better the rate will be, because you will be starting with more equity. You can pay points to lower your interest rate over the term of the loan, meaning you pay more initially. To a lot of people, this is a good option..
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