When you are offered a "rate lock" from your lender, it means that you are guaranteed to keep a particular interest rate for a determined period for your application process. This prevents you from getting through your entire application process and learning at the end that the interest rate has gotten higher.
While there may be a choice of rate lock periods (from 15 to 60 days), the extended ones are typically more expensive. You can get a longer period for your lock, but in doing so, will likely have a higher rate than you would have with a shorter rate lock period
There are more ways to get a better rate, in addition to opting for a shorter rate lock period. The bigger down payment you make, the smaller your interest rate will be, since you will have more equity from the start. You can pay points to bring down your rate for the term of the loan, meaning you pay more up front. To a lot of people, this is a good option..
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