When you are promised a "rate lock" from your lender, it means that you are guaranteed to keep a specific interest rate over a certain number of days while you work on the application process. This prevents you from going through your entire application process and discovering at the end that your interest rate has gotten higher.
Although there can be a choice of rate lock periods (from 15 to 60 days), the extended ones are typically more expensive. You can get a longer period for your lock, but in doing so, will likely have a higher interest rate than you would with a shorter rate lock period
In addition to opting for a shorter rate lock period, there are other ways you may be able to score the best rate. The more the down payment, the better the interest rate will be, because you will have more equity from the start. You could choose to pay points to bring down your interest 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 interest rate over the term of the loan. You'll pay more initially, but you'll save money, especially if you keep the loan for a long time.
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