When you're promised a "rate lock" from the lender, it means that you are guaranteed to get a specific interest rate over a certain number of days while you work on the application process. This means your interest rate can't get higher during the application process.
Although there are various lengths of rate lock periods (from 15 to 60 days), the extended ones are generally more expensive. You can get a longer period for your lock, but in doing so, will most likely have a higher rate than you would have with a shorter rate lock span of time
In addition to going with a shorter lock period, there are several ways you can get the best rate. The more the down payment, the lower the interest rate will be, since you will have more equity from the start. You may choose to pay points to lower your rate over the loan term, meaning you pay more up front. To a lot of people, this makes financial sense..
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