When you're offered a "rate lock" from a lender, it means that you are guaranteed to get a particular interest rate over a certain number of days for the application process. This protects you from getting through your whole application process and finding out at the end that the interest rate has gone up.
Rate lock periods can vary in length, between 15 to 60 days, with the longer period usually costing more. You can get a longer period for your lock, but in choosing this option, will probably have a higher interest rate than you would with a shorter span of time
There are more ways to get a better rate, in addition to opting for a shorter rate lock period. The more the down payment, the better the rate will be, as you will have more equity from the start. You can pay points to bring down your rate over 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 term of the loan. You'll pay more initially, but you will come out ahead, especially if you don't refinance early.
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