A rate "lock" or "commitment" is a lender's promise to lock in a certain interest rate and a certain number of points for you for a certain period while your application is processed. This means your interest rate can't get higher while you are going through the application process.
While there may be a choice of rate lock periods (from 15 to 60 days), the longer ones are generally more expensive. A lending institution can agree to hold 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 that of a rate lock of fewer days.
In addition to choosing the shorter rate lock period, there are more ways you may be able to attain the best rate. A bigger down payment will get you a better interest rate, because you'll be starting out with a good deal of equity. You can pay points to improve your rate over the term of the loan, meaning you pay more initially. For many people, this makes sense and is a good deal..
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