When you're 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 for your application process. This protects you from going through your entire application process and discovering at the end that the interest rate has risen higher.
Rate lock periods can be various lengths of time, anywhere from 15 to 60 days, with the longer period usually costing more. The lender can agree to lock in an interest rate and points for a longer period, such as 60 days, but in exchange, the rate (and sometimes points) will be more than that of a rate lock of fewer days.
There are other ways to get a reduced rate, in addition to opting for a shorter rate lock period. The bigger the down payment, the smaller the interest rate will be, because you will have more equity from the beginning. You might opt to pay points to bring down your rate for the term of the loan, meaning you pay more up front. To many people, this is a good option..
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