When you're promised a "rate lock" from a lender, it means that you are guaranteed to get a set interest rate over a determined period while you work on your application process. This ensures that your interest rate can't go up as you are working through 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. A lending institution will agree to hold an interest rate and points for a longer period, such as 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 lower rate, besides choosing a shorter rate lock period. A larger down payment will result in a reduced interest rate, since you will have a good amount of equity from the beginning. You can pay points to lower your interest rate for the loan term, meaning you pay more up front. To many people, this is a good option..
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