Loan Prepayment Calculator

See how extra payments on your loan cut total interest and shorten the term. Compare the original schedule with the accelerated one.

All calculations happen locally in your browser. Nothing leaves your device.

Original total interest
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Original total paid
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New term (months)
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New total interest
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Interest saved
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Time saved
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New total paid
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How Prepayment Saves Interest

In an equal-principal-and-interest (annuity) loan your monthly payment stays the same, but the split between interest and principal changes every month. Because interest is charged on the remaining balance, early payments are mostly interest. Prepaying extra shrinks that balance sooner, so every later month accrues less interest — the result is a smaller total interest bill and a shorter term.

Why early payments are mostly interest
Interest for a month is the remaining balance times the monthly rate. At the start the balance is the full loan, so the first payment covers almost nothing of the principal. Only as the balance shrinks does the principal share of each payment grow.
Equal-principal-and-interest vs. equal-principal
The annuity (equal-principal-and-interest) method keeps the payment constant while the interest share falls over time. The equal-principal method keeps the principal share constant and lets the payment decline. Prepayment shortens the loan in both, but its impact is strongest in the early months of the annuity method, where interest costs are highest.
Why prepayment saves money
Every extra dollar applied to principal stops generating future interest. The faster the outstanding balance declines, the less interest accrues each month, and the loan is paid off before the original schedule ends — that difference is the money you save.

Frequently Asked Questions

What is the equal-principal-and-interest (annuity) method?

Each period you pay a fixed amount M = P × r × (1+r)^n / ((1+r)^n − 1), where P is the principal, r the monthly rate and n the number of months. The payment never changes, but the interest part of each payment shrinks as the balance falls.

Does prepayment change my regular monthly payment?

In this calculator the extra amount is added to the regular payment, so while you prepay you send M + extra each month. Many banks offer the alternative of keeping the payment unchanged and simply shortening the term; the interest saved is very similar.

How is the final (short) payment handled?

The last payment covers only what is left: the remaining principal plus that month's interest. It is usually smaller than M + extra, and the simulation caps the final payment at the outstanding balance so the total paid never exceeds it.

Does prepaying early save more than prepaying late?

Yes. Interest is charged on the outstanding balance, so a dollar of principal removed early stops generating interest for every remaining month. The same total prepayment made later saves less.

Is my loan data sent to a server?

No. Every number is computed locally in your browser with JavaScript. The page works fully offline once loaded, and nothing you enter is stored or transmitted.