A rate "lock" or "commitment" is a promise from the lender to lock in a particular interest rate and a specific number of points for you for a specified period during your application process. This keeps you from working through your whole application process and learning at the end that your interest rate has gotten higher.
While 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 probably have a higher rate than you would have with a shorter period
There are more ways to get a lower rate, in addition to opting for a shorter rate lock period. The larger down payment you can make, the better the rate will be, because you will have more equity from the start. You might choose to pay points to reduce your interest 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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