When you're promised a "rate lock" from the lender, it means that you are guaranteed to keep a specific interest rate over a determined period while you work on your application process. This protects you from getting through your entire application process and learning at the end that the interest rate has gotten higher.
Rate lock periods can vary in length, between fifteen to sixty days, with the longer period generally costing more. The lending institution may agree to hold an interest rate and points for a longer span of time, such as 60 days, but in exchange, the rate (and sometimes points) will be more than that of a rate lock of a shorter period.
In addition to choosing a shorter rate lock period, there are more ways you can get the lowest rate. A bigger down payment will get you a lower interest rate, because you'll be starting out with more equity. You could choose to pay points to improve your rate over the loan term, meaning you pay more initially. One strategy that is a good option for some is to pay points to bring the rate down 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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