When you're promised a "rate lock" from the lender, it means that you are guaranteed to get a particular interest rate over a determined period while you work on the application process. This prevents you from working through your whole application process and finding out at the end that the interest rate has risen higher.
Rate lock periods can be various lengths of time, between fifteen to sixty days, with the longer period generally costing more. You can get a longer period for your lock, but in choosing this option, will probably have a higher interest rate than you would with a shorter period
There are other ways to get a good rate, in addition to choosing a shorter rate lock period. The larger the down payment, the smaller your rate will be, since you will be starting with more equity. You may opt to pay points to reduce your rate for the term of the loan, meaning you pay more up front. For a lot of people, this makes financial sense..
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