A rate "lock" or "commitment" is a promise from the lender to hold a certain interest rate and a specific number of points for you for a certain period of time while your application is processed. This means your interest rate can't go up as you are going through the application process.
Although there are various lengths of rate lock periods (from 15 to 60 days), the extended ones are typically more expensive. The lender will agree to lock in an interest rate and points for a longer span of time, such as 60 days, but in exchange, the rate (and sometimes points) will be more than that of a rate lock of a shorter period.
In addition to choosing a shorter lock period, there are several ways you may be able to score the best rate. A larger down payment will get you a reduced interest rate, since you're starting out with a good deal of equity. You may opt to pay points to bring down your interest rate for the life of the loan, meaning you pay more up front. To many people, this makes sense and is a good deal..
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