When you are promised a "rate lock" from your lender, it means that you are guaranteed to keep a set interest rate over a certain number of days for your application process. This protects you from getting through your entire application process and discovering at the end that your interest rate has gotten higher.
Although there may be a choice of rate lock periods (from 15 to 60 days), the extended ones are usually 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 rate lock period, there are several ways you can score the lowest rate. A larger down payment will give you a lower interest rate, because you'll be starting out with more equity. You can pay points to reduce your interest rate over the loan term, meaning you pay more up front. For a lot of people, this is a good option..
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