When you are promised a "rate lock" from a lender, it means that you are guaranteed to get a specific interest rate over a certain number of days while you work on your application process. This means your interest rate can't go up during the application process.
While there are several lengths of rate lock periods (from 15 to 60 days), the longer ones are generally more expensive. You can get a longer period for your lock, but in choosing this option, will most likely have a higher interest rate than you would with a shorter rate lock period
There are other ways to get a good rate, in addition to agreeing to a shorter rate lock period. A bigger down payment will give you a reduced interest rate, because you will have a good deal of equity at the start. You can pay points to reduce your interest rate over the loan term, meaning you pay more initially. One strategy that is a good option for some is to pay points to reduce the rate over the term of the loan. You'll pay more up front, but you'll come out ahead in the end.
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