A rate "lock" or "commitment" is a promise from the lender to hold a particular interest rate and a certain 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 learning at the end that your interest rate has risen higher.
Although there might be a choice of rate lock periods (from 15 to 60 days), the extended spans are typically more expensive. You can get a longer period for your lock, but in choosing this option, will likely have a higher rate than you would with a shorter period
In addition to going with the shorter rate lock period, there are more ways you can attain the lowest rate. The larger down payment you can make, the smaller the interest rate will be, because you will have more equity from the beginning. You can pay points to bring down your interest rate over the loan term, meaning you pay more up front. To many people, this makes financial sense..
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