Making an additional principal payment can help borrowers pay off a loan more quickly than sticking to the regular minimum payment schedule. When obtaining a loan, borrowers receive an amortization table, which lists each monthly payment and how much of the payment goes toward interest and how much reduces the principal balance. Because extra payments go straight toward principal, they change the remainder of the amortization table and bring the loan payoff date closer. You can use an online loan calculator to obtain your new amortization table and loan payoff date.

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     Look up information about your loan terms, including the original loan amount, date on which the loan was taken out, interest rate and the number of monthly payments in the original payment schedule. The number of monthly payments is also equal to the number of years of repayment times 12 months.

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     Go to Bankrate.com's online loan calculator (see References).

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     Type the information about your loan into the loan calculator. For example, your loan may be a mortgage of $165,000 with a term of 30 years, interest rate of 7 percent per year and start date of April 1, 2005.

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     Click the "Calculate" button to show your monthly payment, which in this example is $1,097.75.

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     Type in the amount of your additional principal payment and the date on which the payment was made or will be made. For example, you may have made a principal payment of $5,000 in October 2010.

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     Click the button to show the amortization table.

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     Scroll to the bottom of the amortization table to find your loan payoff date. In this example, your last payment will be in May 2033, which is 23 months earlier than the originally scheduled end date in April 2035. Notice that although the additional payment amount was slightly less than five monthly payments, it had a significantly larger impact in accelerating the payment of the loan.