When you're offered a "rate lock" from the lender, it means that you are guaranteed to keep a specific interest rate over a certain number of days while you work on your application process. This prevents you from working through your entire application process and discovering at the end that your interest rate has gotten higher.
While there are several lengths of rate lock periods (from 15 to 60 days), the extended spans 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 with a shorter period
In addition to choosing a shorter rate lock period, there are other ways you are able to get the best rate. The larger down payment you can pay, the lower the interest rate will be, since you will have more equity from the start. You could opt to pay points to improve your interest rate for the loan term, meaning you pay more initially. 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 initially, but you will come out ahead, especially if you keep the loan for the full term.
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