Pay Off a Loan With Extra Payments Calculator

This calculator estimates how many months it takes to repay a loan when you make a fixed monthly payment above the regular amount. Enter the balance, APR, and the extra amount you plan to pay each month to see the estimated payoff time and total interest.

Formula

The calculator first finds the regular monthly payment for a 60-month loan, rounded to the nearest cent, then adds the extra monthly payment. It estimates the number of monthly payments needed to repay the balance using the standard level-payment payoff formula:

Regular payment: PMT = round[P × r ÷ (1 − (1 + r)⁻ⁿ), 2]

Months to payoff: m = ceil[round(−ln(1 − r × P ÷ A) ÷ ln(1 + r), 6)]

Total paid: T = A × m; interest paid: I = T − P.

• P is the current loan balance in dollars.
• APR is the annual percentage rate, entered as a percentage; r is the monthly rate, APR ÷ 1,200.
• n is the assumed original repayment period of 60 months.
• PMT is the regular monthly payment in dollars, rounded to cents.
• A is PMT plus the extra monthly amount, in dollars.
• m is the estimated number of monthly payments, rounded up to a whole month.
• T and I are estimated total dollars paid and interest dollars paid.

This setup treats the extra amount as recurring every month. It does not calculate a one-time lump-sum payment. The calculator uses the stated balance as the loan principal for its estimate, so enter the current payoff balance if you have it rather than the original amount borrowed.

Worked Example

Using the defaults: balance P = $20,000, APR = 8%, extra monthly payment = $200, and assumed term n = 60 months.

1. Convert the APR to a monthly rate: r = 8 ÷ 1,200 = 0.0066667.
2. Calculate the regular payment: PMT = round[$20,000 × 0.0066667 ÷ (1 − (1.0066667)⁻⁶⁰), 2] = $405.53.
3. Add the extra amount: A = $405.53 + $200 = $605.53.
4. Calculate payoff time: m = ceil[round(−ln(1 − 0.0066667 × 20,000 ÷ 605.53) ÷ ln(1.0066667), 6)] = 38 months.
5. Estimate total paid: T = $605.53 × 38 = $23,010.14.
6. Estimate interest: I = $23,010.14 − $20,000 = $3,010.14.

Because the formula uses a constant monthly payment for all 38 months, the final payment may be smaller than $605.53 in actual servicing. The total is therefore a consistent estimate under the stated assumptions, not a precise payment schedule.

Assumptions

• The APR is fixed for the estimate.
• Payments are made monthly, with the regular payment and extra amount treated as one level payment.
• Interest compounds monthly at APR ÷ 12; payment timing is approximated by a standard monthly amortization formula.
• The assumed regular-payment term is 60 months because this calculator does not ask for the loan’s original term or current required payment.
• Fees, taxes, insurance, PMI, escrow, late charges, and lender-specific payment allocation are not included.

When to Use an Extra-Payment Calculator

Use this estimate to understand how a recurring additional payment might change the repayment timeline and the amount of interest implied by a fixed-rate amortization model. It can help frame questions to ask a loan servicer, such as whether extra funds are applied to principal, whether instructions are needed, and whether the lender recalculates the required payment after a principal reduction.

The calculator’s regular payment is based on a 60-month term, not on the actual required payment shown on your statement. If your loan has a different term or payment amount, the estimate can differ substantially. For a closer result, use the actual current balance, actual APR, and current required payment in a calculator designed to accept that payment, or request a dated payoff quote from the servicer.

How to Read the Results

“Months to payoff” is a whole-month estimate, rounded up because a partial payment period still falls within a final payment month. To translate months into a rough calendar duration, divide by 12; the exact payoff date depends on the next due date and how the servicer processes payments.

“Estimated total paid” multiplies the calculated monthly amount by the estimated number of months. “Estimated interest paid” subtracts the entered balance from that total. These totals assume the same payment every month, including the final month. In practice, the last payment is generally adjusted to the amount still owed, while daily interest, payment dates, rounding, and fees can affect the result.

Common Problems and Limits

• Confusing extra payment with total payment: The input is the extra amount on top of the modeled regular payment, not the whole amount you send each month.
• Using the original loan amount: If payments have already been made, the outstanding balance is usually lower than the amount first borrowed. An up-to-date balance gives a more relevant estimate.
• Assuming every loan is fixed-rate: Variable rates, changing payments, interest-only periods, and balloon payments do not follow this calculation.
• Ignoring payment rules: A lender may handle payments above the required amount differently from the model. Confirm how additional funds are credited and whether any restrictions or charges apply.
• Expecting a precise final payment: The formula estimates full level-payment months; it does not build a daily-interest schedule or calculate a smaller final installment.

The formula also requires the total modeled payment to exceed the monthly interest charge. If it does not, the balance will not amortize under this model. A payment that barely exceeds interest can produce a very long payoff period, so check the result against the payment terms and figures supplied by the servicer.

Frequently Asked Questions

Does an extra payment go directly to principal?
Not necessarily. The calculator assumes the extra amount reduces the balance through the normal amortization process, but the servicer’s payment-allocation rules determine how funds are applied. Check the loan documents or ask the servicer.

Can I enter a one-time extra payment?
No. This calculator treats the extra amount as a recurring monthly addition. A lump-sum payment changes the balance at a particular time and needs a calculation that accounts for its date.

Why does the calculator use a 60-month term?
The regular payment must be estimated from a term, and this calculator fixes that assumption at 60 months rather than asking for the actual term or required payment. If your loan differs, the estimated payoff period and totals may not match your account.

Does paying extra always reduce interest?
In a standard fixed-rate amortizing model, reducing principal sooner generally reduces the interest calculated in later periods. Actual results depend on the loan’s terms, payment processing, fees, and whether the extra funds are applied to principal.

Why is the final payment different from the amount shown?
The estimate counts whole months at one fixed payment. A real final installment is often adjusted to cover the remaining principal and accrued interest, and its amount depends on payment timing and servicing calculations.

This result is an estimate, and the lender’s disclosure gives the exact figures.

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in p | Loan balance | $ | 20000 | 0.01 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in extra | Extra monthly payment | $ | 200 | 0 | 100000000
out months | Months to payoff | months | ceil(round(-ln(1 - (apr / 1200) * p / (p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -60) + extra)) / ln(1 + apr / 1200), 6)) | 0
out total | Estimated total paid | $ | (p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -60) + extra) * months | 2
out int | Estimated interest paid | $ | total - p | 2