When you're promised a "rate lock" from your lender, it means that you are guaranteed to keep a certain interest rate for a certain number of days while you work on the application process. This means your interest rate can't go up during the application process.
Rate lock periods can be various lengths of time, anywhere from 15 to 60 days, with the longer period typically costing more. You can get a longer period for your lock, but in doing so, will probably have a higher interest rate than you would have with a shorter rate lock period
In addition to going with the shorter lock period, there are other ways you may be able to get the lowest rate. A bigger down payment will get you a better interest rate, since you will have a good deal of equity from the beginning. You might choose to pay points to bring down your rate for the loan term, meaning you pay more up front. To a lot of people, this makes sense and is a good deal..
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