When you're offered a "rate lock" from a lender, it means that you are guaranteed to keep a set interest rate for a certain number of days for the application process. This saves you from going through your whole application process and learning at the end that your interest rate has gone up.
Rate lock periods can vary in length, between fifteen to sixty days, with the longer period usually costing more. You can get a longer period for your lock, but in choosing this option, will likely have a higher rate than you would have with a shorter span of time
In addition to choosing the shorter lock period, there are more ways you can get the lowest rate. The bigger down payment you pay, the lower your rate will be, because you will have more equity from the beginning. You could opt to pay points to reduce your rate for the life of the loan, meaning you pay more up front. One strategy that makes financial sense for some is to pay points to bring the rate down over the life of the loan. You'll pay more up front, but you will save money, especially if you don't refinance early.
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