When you are promised a "rate lock" from a lender, it means that you are guaranteed to keep a certain interest rate for a determined period while you work on your application process. This saves you from working through your entire application process and finding out at the end that your interest rate has risen higher.
Although there might be a choice 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 making this choice, will likely have a higher rate than you would with a shorter rate lock span of time
There are more ways to get a low rate, besides choosing a shorter rate lock period. The bigger down payment you can make, the lower your interest rate will be, since you will have more equity from the start. You may choose to pay points to improve your rate over the life of the loan, meaning you pay more up front. One strategy that makes financial sense for many people is to pay points to improve the rate over the term of the loan. You will pay more initially, but you will save money in the end.
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