When you are promised a "rate lock" from a lender, it means that you are guaranteed to get a certain interest rate over a determined period for your application process. This keeps you from working through your entire application process and discovering at the end that your interest rate has gotten higher.
Rate lock periods can be various lengths of time, between 15 to 60 days, with the longer ones generally costing more. The lending institution will agree to lock in an interest rate and points for a longer span of time, like sixty days, but in exchange, the rate (and sometimes points) will be higher than with a rate lock of a shorter period.
In addition to choosing the shorter lock period, there are several ways you can attain the best rate. A larger down payment will give you a lower interest rate, since you will have a good deal of equity from the beginning. You can pay points to bring down your 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 interest rate over the life of the loan. You'll pay more initially, but you'll save money in the long run.
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