When you're offered a "rate lock" from a lender, it means that you are guaranteed to keep a specific interest rate over a determined period while you work on your application process. This protects you from going through your entire 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 ones usually costing more. A lender will agree to hold an interest rate and points for a longer period, say sixty days, but in exchange, the rate (and sometimes points) will be more than with a rate lock of a shorter period.
There are more ways to get a better rate, besides opting for a shorter rate lock period. A larger down payment will result in a lower interest rate, because you'll be starting out with a good deal of equity. You may choose to pay points to improve your rate for the term of the loan, meaning you pay more initially. One strategy that makes financial sense for some is to pay points to improve the rate over the term of the loan. You will pay more up front, but you will save money in the long run.
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