When you're promised a "rate lock" from a lender, it means that you are guaranteed to get a set interest rate over a certain number of days while you work on your application process. This ensures that your interest rate cannot get higher as you are going through the application process.
Rate lock periods can be various lengths of time, anywhere from fifteen to sixty days, with the longer ones generally costing more. You can get a longer period for your lock, but in choosing this option, will probably have a higher rate than you would have with a shorter rate lock period
There are more ways to get a low rate, besides agreeing to a shorter rate lock period. A larger down payment will result in a reduced interest rate, since you will be starting out with more equity. You could choose to pay points to reduce your interest rate for the loan term, meaning you pay more up front. One strategy that is a good option for many people is to pay points to bring the rate down over the life of the loan. You'll pay more initially, but you will save money, especially if you don't refinance early.
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