A rate "lock" or "commitment" is a lender's promise to freeze a particular interest rate and a specific number of points for you for a certain period while your application is processed. This keeps you from going through your entire application process and learning at the end that the interest rate has gotten higher.
Although there can be a choice of rate lock periods (from 15 to 60 days), the extended ones are usually more expensive. The lender can agree to hold 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 fewer days.
There are more ways to get a lower rate, in addition to agreeing to a shorter rate lock period. A bigger down payment will give you a reduced interest rate, because you will be starting out with more equity. You might choose to pay points to reduce your rate for the loan term, meaning you pay more up front. One strategy that is a good option for some is to pay points to bring the rate down over the life of the loan. You pay more initially, but you will save money, especially if you don't refinance early.
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