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 of time during your application process. This protects you from working through your whole application process and discovering at the end that your interest rate has risen higher.
While there may be a choice of rate lock periods (from 15 to 60 days), the extended ones are typically more expensive. You can get a longer period for your lock, but in choosing this option, will probably have a higher rate than you would have with a shorter rate lock span of time
There are more ways to get a reduced rate, besides going with a shorter rate lock period. A bigger down payment will give you a lower interest rate, since you will be starting out with a good deal of equity. You may choose to pay points to bring down your interest rate over the life of the loan, meaning you pay more up front. For a lot of people, this is a good option..
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