When you're promised a "rate lock" from your lender, it means that you are guaranteed to keep a set interest rate over a certain number of days while you work on the application process. This saves you from going through your entire application process and discovering at the end that your interest rate has risen higher.
While there are several lengths of rate lock periods (from 15 to 60 days), the longer spans are usually more expensive. A lending institution may agree to freeze an interest rate and points for a longer period, like 60 days, but in exchange, the rate (and sometimes points) will be higher than that of a rate lock of fewer days.
In addition to opting for a shorter rate lock period, there are more ways you may be able to attain the best rate. A larger down payment will get you a better interest rate, since you will be starting out with a good deal of equity. You can pay points to bring down your rate for the loan term, meaning you pay more initially. One strategy that is a good option for some is to pay points to improve the interest rate over the term of the loan. You'll pay more up front, but you will come out ahead in the long run.
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