A rate "lock" or "commitment" is a promise from the lender to hold a particular interest rate and a particular number of points for you for a specified period while your application is processed. This prevents you from getting through your whole application process and discovering at the end that the interest rate has gone up.
Rate lock periods can be various lengths of time, between 15 to 60 days, with the longer spans generally costing more. You can get a longer period for your lock, but in making this choice, will likely have a higher interest rate than you would with a shorter span of time
There are other ways to get a better rate, in addition to going with a shorter rate lock period. A larger down payment will get you a better interest rate, because you'll have a good amount of equity at the start. You could opt to pay points to bring down your rate for the term of the loan, meaning you pay more initially. To a lot of people, this is a good option..
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