A lock, also called a rate lock or rate commitment, is a lender's promise to hold a certain interest rate and a certain number of points for you, usually for a specified period of time, while your loan application is processed. Depending upon the lender, you may be able to lock in the interest rate and number of points that you will be charged when you file your application, during processing of the loan, when the loan is approved, or later.

Shorter loans, such as a 20 year or 15 year note, can save you thousand of dollars in interest payments over the life of the loan, but your monthly payments will be higher. An adjustable rate mortgage may get you started with a lower interest rate than a fixed rate mortgage, but your payments could get higher when the interest rate changes.

A larger down payment greater than 20% will give you the best possible rate. With a down payment of 5% or less, you should expect to pay a higher rate as you are starting with less equity as collateral. If you've got the cash now and want to lower your payments, you can pay points on your loan to lower your mortgage rate. It's a simple concept, really. In exchange for more money up front, lenders are willing to lower the interest rate they charge, cutting the borrower's payments. Closing costs are fees paid by the lender, if you do not want to pay all of the closing costs, expect a higher rate which will pay the lender additional interest over the life of the loan.

Your credit quality and debt-to-income ratio affect the terms of your loan through your FICO Score. If you have good credit and your monthly income far surpasses your monthly debt obligations, you will get approved at a lower interest rate. However, if your monthly income barely covers your minimum debt obligations, even if you have a good credit report, you will not receive the lowest available interest rate.