When you are promised a "rate lock" from your lender, it means that you are guaranteed to get a particular interest rate over a determined period for the application process. This means your interest rate won't go up during the application process.
Rate lock periods can vary in length, anywhere from fifteen to sixty days, with the longer period typically costing more. You can get a longer period for your lock, but in doing so, will likely have a higher interest rate than you would have with a shorter period
There are other ways to get a lower rate, in addition to going with a shorter rate lock period. A bigger down payment will get you a reduced interest rate, since you will have a good amount of equity at the start. You can pay points to improve your interest rate for the loan term, meaning you pay more up front. For a lot of people, this is a good option..
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