What is a "rate lock period"? How can you make sure your rate is low?

A rate lock or a rate commitment is a lender's promise to hold a certain interest rate and a certain number of points for you for a specified period of time while your application is processed. This prevents you from going through your whole application process and at the end of it finding out the interest rate has gone up.

A rate lock period can vary in length, and longer ones usually cost more. A lender will agree to "hold" your interest rate and points for a longer period, say 60 days, but in exchange the rate and maybe points are higher than with a shorter rate lock period, for example.

There are many ways besides opting for a shorter rate lock period to get a lower rate, though. A larger down payment may result in a lower interest rate than a smaller one, because you're starting out with more equity. Strong credit may result in a lower interest rate than weak credit, because you're considered less risky. And you can pay points to lower your rate over the life of the loan, but that means you pay more up front. (For some people it makes sense to buy down the rate by paying discount points, if they need a lower rate to qualify. But if you sell or refinance before the loan matures, typically 30 years, then you don't fully realize the benefits of any points you pay up front.)