Q. We’re in the fifth year of a 15 year mortgage and have come into some extra money. How can I figure out if paying $2,000 extra will shorten my payments and is the best thing to do? We are paying 6% interest on the mortgage and can only get about 4% interest on any short term CD.

A.You didn’t provide us with exact figures on your mortgage, but consider this example. If you had 10 years, six months left at 6% and a balance of $70,000, your payments would be $750 a month for principal and interest. You’d finish paying the loan off in May 2017 at a total cost of $24,519 in interest over the next decade.

If you made a one-time payment of $2,000, you would finish paying your mortgage in January 2017 and you’d pay $22,825 in interest, saving yourself four months and almost $1,700.

To calculate this yourself, using your real numbers, use our loan payment calculator. Just enter your balance, the years left on your mortgage, and your interest rate. Then below, where it says "extra payments" put in your $2000 as a one-time payment and then hit "Show amortization schedule." Look at the "payoff date" and then scroll to the bottom of the amortization schedule and check the "total interest payments." That's your real payoff.

There are a lot of banks offering 5.25% or more on 6-month and 12-month CDs.

If you were able to invest that $2,000 at 5% over the same 10-year period you’d make about $1,300 in interest. You’d have to earn about 6.5% to match the $1.700 you’d save by making an early payment on your loan.