When you're promised a "rate lock" from your lender, it means that you are guaranteed to get a set interest rate for a certain number of days for the application process. This ensures that your interest rate will not go up as you are going through the application process.
While there may be a choice of rate lock periods (from 15 to 60 days), the extended spans are generally more expensive. You can get a longer period for your lock, but in making this choice, will most likely have a higher rate than you would have with a shorter period
There are other ways to get a good rate, besides opting for a shorter rate lock period. A larger down payment will result in a reduced interest rate, since you are starting out with a good deal of equity. You can pay points to lower your interest rate over the term of the loan, meaning you pay more initially. One strategy that is a good option for some is to pay points to improve the rate over the life of the loan. You are paying more up front, but you will come out ahead in the end.
Do you have a question regarding a mortgage program?