When you are promised a "rate lock" from your lender, it means that you are guaranteed to get a particular interest rate for a certain number of days while you work on the application process. This means your interest rate won't get higher while you are going through the application process.
While there may be a choice of rate lock periods (from 15 to 60 days), the extended ones are typically more expensive. The lending institution may agree to hold an interest rate and points for a longer span of time, like 60 days, but in exchange, the rate (and sometimes points) will be higher than with a rate lock of fewer days.
In addition to opting for the shorter lock period, there are more ways you can get the lowest rate. The bigger down payment you make, the better the rate will be, because you will have more equity from the start. You could opt to pay points to bring down your rate over the life of the loan, meaning you pay more up front. For many people, this makes sense and is a good deal..
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