When you're offered a "rate lock" from your lender, it means that you are guaranteed to keep a particular interest rate for a certain number of days while you work on the application process. This means your interest rate cannot rise during the application process.
While there might be a choice 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 choosing this option, will likely have a higher interest rate than you would have with a shorter rate lock period
There are other ways to get a reduced rate, in addition to going with a shorter rate lock period. A bigger down payment will result in a reduced interest rate, because you are starting out with more equity. You can pay points to bring down your interest rate for the term of the loan, 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'll pay more up front, but you'll come out ahead in the end.
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