The scheduled payment pays interest first and then reduces principal. Extra payments reduce principal sooner, so later interest is calculated on a smaller balance; the payoff comparison quantifies that time and cost difference.
Confirm that the lender applies extra money to principal and does not charge a prepayment penalty. Fees included in APR may not be represented in the amortized balance entered here.
Monthly payment and total interest on auto, student and personal loans
Standard amortization gives the monthly payment on auto, student and personal loans, alongside the declining balance and the interest you accumulate. Add an extra monthly payment to see how much sooner the loan clears.
The scheduled payment pays interest first and then reduces principal. Extra payments reduce principal sooner, so later interest is calculated on a smaller balance; the payoff comparison quantifies that time and cost difference.
Confirm that the lender applies extra money to principal and does not charge a prepayment penalty. Fees included in APR may not be represented in the amortized balance entered here.
UNDERSTAND THE NUMBERS
Fixed educational example · independent of your inputs above. $ means US dollars; these are not current rate quotes or return forecasts.
Borrow $20,000 at a fixed 8% annual rate for five years. Compare the scheduled payment with an additional $100 every month from the first payment. No origination or early-repayment fees are included.
| Monthly payment | Payoff time | Total interest |
|---|---|---|
| $405.53 | 60 months | $4,331.67 |
| $505.53 | 47 months | $3,295.30 |
The extra-payment scenario saves $1,036.37 of modeled interest and finishes 13 months sooner. The last payment can be smaller than the regular amount because only the remaining balance and interest are due.
The calculator divides the entered annual rate by 12. A disclosed APR that includes fees may differ from the contractual interest rate used to calculate installments. Confirm that extra payments reduce principal and check the lender's actual repayment terms.
Try $25, $50 and $100 of extra repayment. Compare the interest reduction with how much monthly flexibility each option leaves, keeping the original term and rate unchanged.
Model a balance with a fixed monthly payment →Prepared by EconoPi · examples and explanations reviewed September 19, 2026. Tables are our calculations under stated assumptions, not forecasts or recommendations by the referenced organizations.
The amortization formula P × r / (1 − (1+r)^−n), where r is the monthly rate and n the number of months.
Every extra dollar comes straight off principal, so the interest it would have carried disappears too. The earlier you do it, the bigger the saving.
APR can include certain loan fees, while the contractual interest rate determines interest charged on the balance. This calculator simply divides the entered annual rate by 12 and does not separately reproduce fee-inclusive APR disclosures.
It is total interest divided by the initial principal. Compare it across the same loan amount and inspect term length, monthly affordability and any refinancing costs separately; there is no universal cutoff.
All math runs in your browser and your inputs are never sent to a server. Settings are saved locally and share links encode the state in the URL. For information only — not investment or tax advice.