A rate "lock" or "commitment" is a lender's promise to set a particular interest rate and a certain number of points for you for a specified period while your application is processed. This keeps you from going through your whole application process and finding out at the end that the interest rate has risen higher.
Although there might be a choice of rate lock periods (from 15 to 60 days), the extended ones are usually more expensive. 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 rate lock 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 make, the better your interest rate will be, because you will have more equity from the beginning. You may opt to pay points to improve your rate for the loan term, meaning you pay more up front. To a lot of people, this makes financial sense..
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