When you are promised a "rate lock" from the lender, it means that you are guaranteed to keep a certain interest rate over a determined period for the application process. This prevents you from getting through your entire application process and discovering 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 longer spans are usually more expensive. You can get a longer period for your lock, but in making this choice, will probably have a higher interest rate than you would with a shorter period
In addition to choosing a shorter rate lock period, there are other ways you can score the best rate. The larger down payment you can pay, the lower the rate will be, since you will be starting with more equity. You can pay points to improve your interest rate for the loan term, meaning you pay more up front. To many people, this makes financial sense..
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