A rate "lock" or "commitment" is a promise from the lender to set a certain interest rate and a particular number of points for you for a specified period while your application is processed. This protects you from working through your whole application process and discovering at the end that your interest rate has risen higher.
Rate lock periods can vary in length, between fifteen to sixty days, with the longer period typically costing more. The lending institution will agree to hold an interest rate and points for a longer span of time, say 60 days, but in exchange, the rate (and sometimes points) will be more than that of a rate lock of fewer days.
There are more ways to get a good rate, besides agreeing to a shorter rate lock period. A larger down payment will give you a reduced interest rate, because you'll have a good deal of equity from the beginning. You may choose to pay points to improve your rate over the term of the loan, meaning you pay more initially. To many people, this is a good option..
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