When you're offered 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 ensures that your interest rate won't go up during the application process.
While there might be a choice of rate lock periods (from 15 to 60 days), the longer ones are typically more expensive. The lender may agree to lock in an interest rate and points for a longer span of time, such as sixty days, but in exchange, the rate (and sometimes points) will be higher 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 bigger down payment will give you a reduced interest rate, since you'll have more equity at the start. You can pay points to reduce your rate for the loan term, meaning you pay more up front. For a lot of people, this makes sense and is a good deal..
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