A rate "lock" or "commitment" is a lender's promise to freeze a certain interest rate and a specific number of points for you for a certain period of time during your application process. This means your interest rate won't rise during the application process.
While there may be a choice of rate lock periods (from 15 to 60 days), the extended ones are generally more expensive. You can get a longer period for your lock, but in doing so, will likely have a higher rate than you would have with a shorter span of time
In addition to going with a shorter lock period, there are more ways you are able to get the lowest rate. A larger down payment will result in a better interest rate, since you will have more equity from the beginning. You could opt to pay points to bring down your interest rate over the term of the loan, meaning you pay more initially. To many people, this makes financial sense..
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