When you're offered a "rate lock" from the lender, it means that you are guaranteed to keep a certain interest rate over a determined period for your application process. This saves you from getting through your whole application process and learning at the end that your interest rate has gone up.
Although there are various lengths of rate lock periods (from 15 to 60 days), the extended spans are generally more expensive. The lending institution will agree to hold an interest rate and points for a longer period, 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.
There are other ways to get a good rate, besides choosing a shorter rate lock period. The bigger down payment you can pay, the smaller the interest rate will be, because you will be starting with more equity. You can pay points to bring down your interest rate over 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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