When you're offered a "rate lock" from a lender, it means that you are guaranteed to get a particular interest rate over a certain number of days for your application process. This keeps you from getting through your entire application process and learning at the end that your interest rate has risen higher.
While there might be a choice of rate lock periods (from 15 to 60 days), the longer ones are usually more expensive. You can get a longer period for your lock, but in making this choice, will probably have a higher rate than you would have with a shorter rate lock period
In addition to choosing a shorter lock period, there are several ways you can attain the best rate. A bigger down payment will get you a lower interest rate, because you will have a good amount of equity at the start. 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 many people is to pay points to improve the interest rate over the life of the loan. You will pay more initially, but you'll come out ahead, especially if you keep the loan for a long time.
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