When you are promised a "rate lock" from a lender, it means that you are guaranteed to get a certain interest rate for a certain number of days for the application process. This ensures that your interest rate won't grow during the application process.
Rate lock periods can vary in length, between 15 to 60 days, with the longer spans usually costing more. 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 more ways to get a lower rate, in addition to going with a shorter rate lock period. The more the down payment, the better the rate will be, because you will have more equity from the start. You may choose to pay points to bring down your interest rate for the life of the loan, meaning you pay more up front. One strategy that makes financial sense for some is to pay points to improve the rate over the life of the loan. You'll pay more up front, but you'll come out ahead, especially if you don't refinance early.
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