Paying one-half of your regular monthly mortgage payment every two weeks can shave six to eight years off a typical 30-year fixed mortgage. That’s because you end up making the equivalent of 13 monthly mortgage payments a year instead of 12, and the extra payment goes toward you principal.

But there’s no need to pay your mortgage company or anyone else to put you on a bi-weekly program. You can do it yourself. Just ask your lender if you can send in half-payments every two weeks without enrolling in a bi-weekly program. If the lender says no, you can accomplish the same goal by adding one-twelfth of your normal payment to your mortgage each month and noting that the extra should go toward principal. Many lenders will you do this with an automatic payment program.

Just make sure that accelerated payment schedule will not result in a prepayment penalty.

For more, see http://www.bankrate.com/brm/news/mtg/20010920a.asp

This calculator http://www.decisionaide.com/mpcalculators/ExtraPaymentsCalculator/ExtraPayments1.asp lets you how much you can save by paying your mortgage bi-weekly or making extra principal payments.