When you're offered a "rate lock" from the lender, it means that you are guaranteed to get a specific interest rate for a determined period while you work on the application process. This keeps you from getting through your entire application process and discovering at the end that the interest rate has gone up.
Rate lock periods can vary in length, anywhere from 15 to 60 days, with the longer spans generally costing more. You can get a longer period for your lock, but in doing so, will probably have a higher rate than you would with a shorter rate lock span of time
In addition to opting for a shorter lock period, there are other ways you can attain the lowest rate. The larger down payment you can make, the lower the rate will be, because you will be entering the loan with more equity. You could opt to pay points to improve your rate over the term of the loan, meaning you pay more up front. One strategy that makes financial sense for some is to pay points to improve the rate over the life of the loan. You'll pay more up front, but you will save money in the long run.
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