Paying extra on your mortgage can be a good idea.

It can shave years off your loan and save tens of thousands of dollars in interest charges.

Before you start, our 3 things you must do before paying extra on your mortgage can help you make sure it's the best use of your money.

The one thing you should not do is sign up for an accelerated payment plan from a mortgage service company that costs hundreds of dollars a year.

There are several free and easy ways to pay off your mortgage faster by making the equivalent of 13 mortgage payments a year instead of the standard 12.

Increase your monthly checks by one-twelfth. The additional money reduces your mortgage balance.

Make one extra payment a year. This works especially well if you get an annual bonus or always receive a sizable income tax refund. Just add the money to your next monthly payment.

Pay half of your regular monthly mortgage payment every two weeks. Although a few mortgage companies allow customers to switch to biweekly payments at no charge, most won't do that, nor will they accept partial payments. But you can have the money automatically transferred from your checking account to a special savings account every two weeks and then transferred to your lender at the end of every month. Ask a representative of your bank or credit union for help setting up online transactions, if necessary.

Caution: Paying down the principal on your loan more quickly will never reduce the minimum monthly payment or allow you to skip a payment.

It simply shortens the length of the loan and reduces the total amount of interest you have to pay.

How much could you save?

A typical $200,000 loan at 6.25% would take 30 years to repay and cost $243,316 in interest with the traditional 12 payments a year. Make the equivalent of 13 monthly payments every year, and the loan will be retired in 24 years and you pay only about $188,000 in interest -- a savings of $55,316.

Of course, you don't have to keep your loan for decades to benefit from extra payments.

You'll immediately begin adding to your equity (the difference between what your home is worth and how much you owe on your mortgages). That lets you ditch private mortgage insurance sooner, saving you as much as a couple hundred dollars a month.

If you ever have an emergency, you'll have enough equity to take out a home equity loan. And, of course, the less you owe on your mortgage, the more money you pocket if you sell your home.

Our accelerated mortgage payoff calculator can figure out how quickly you can pay off your mortgage and how much you'll save.

The biggest obstacle to following through with a faster mortgage payoff plan is self-discipline. It's easy to start paying extra -- until you have extra expenses or you forget an extra payment.

That's where mortgage service companies say they can help. When you buy an accelerated, biweekly payment plan from a mortgage service company, you're essentially asking it to make you pay off your mortgage early. They collect your biweekly checks and fine you if you miss one of your voluntary payments.

They say the threat of those penalties, and the hundreds of dollars they charge in set-up and maintenance fees, are worth it to save tens of thousands of dollars in the long run.

But it's not.

Start-up fees range from $150 to $350 or more. Many companies also charge processing fees of anywhere from $2.50 to $10, plus monthly or annual maintenance fees. Some service companies pay interest on the money they're holding, but that won't come close to covering the fees.

If you pay a $250 initial fee and then $10 a month, you'll spend $370 in the first year and $2,650 over 20 years. If you don't make all 26 payments a year on time, you'll have late fees added on to that and wind up paying even more.

That's the kind of help you don't need.

By Sally Herigstad

Interest.com Contributing Editorinterest.com