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 being processed.  This protects you from any rise in interest rates throughout the application process.

A rate lock period can vary in length from 15 to 30, 45, 60 and even 90 days. Locking a rate for a longer period usually costs more. A lender will agree to "hold" your interest rate and points for a longer period, say 60 days, and in exchange, the rate and points are higher than with a shorter rate lock period. 

There are many ways besides opting for a shorter rate lock period to get a lower rate, though. For example, a larger down payment will result in a lower interest rate than a smaller one, because you're starting out with more equity. You can pay points to lower your rate over the life of the loan, which means that you pay more up front. If you are planning to stay in the house for many years, paying points can be a good choice.

Closing costs are fees paid by the lender, which the lender in turn charges you to close the loan. Many people pay closing costs when they sign on the dotted line, but many finance their closing costs. Paying closing costs when the loan closes will reduce your interest rate.

Finally, the interest rate a lender is willing to offer you depends on your credit score and your income-to-debt ratio. If you have good credit and your income far exceeds your debt obligations, you will qualify for a lower rate.