When you are promised a “rate lock” from your lender, it means that you are guaranteed to get a specific interest rate for a certain number of days while you work on your application process. This protects you from going through your whole application process and finding out at the end that your interest rate has gone up.
While there are various lengths of rate lock periods (from 15 to 60 days), the longer spans are usually more expensive. The lending institution will agree to lock in an interest rate and points for a longer period, say sixty days, but in exchange, the rate (and sometimes points) will be higher than that of a rate lock of fewer days.
Other Ways to Save on Interest
In addition to going with the shorter lock period, there are more ways you are able to get the lowest rate. The larger the down payment, the better your rate will be, because you will be starting with more equity. You can pay points to reduce your interest rate for the loan term, meaning you pay more initially. One strategy that makes financial sense for some is to pay points to bring the rate down over the life of the loan. You pay more initially, but you will save money in the end.