Calculate Loan Payoff Date With Extra Payments

Estimate when a fixed-rate loan will be paid off by entering its balance, APR, regular monthly payment, and extra amount paid each month. The calculator returns the number of months until payoff and the estimated final payment date, using a starting date you choose.

Formula

The estimate assumes the same combined payment each month until the final, smaller payment. The number of months is calculated as:

n = ceil[−ln(1 − rB/M) / ln(1 + r)]

• B is the current loan balance in dollars.
• APR is the annual percentage rate entered as a percent per year.
• r = APR / 1200 is the monthly interest rate as a decimal.
• M = regular payment + extra payment, in dollars per month.
• n is the estimated number of monthly payments; the ceiling function rounds up to a whole month.

The payoff month is found by adding n − 1 months to the first payment month, because the first payment occurs in that starting month. The final-payment estimate applies one month of interest to the remaining balance after n − 1 full payments, then pays it off. Calendar output is shown as year.month; for example, 2027.03 means March 2027. It does not identify a particular day within that month.

Worked Example

Using the calculator’s defaults: balance B = $20,000, APR = 8%, regular payment = $500, extra payment = $100, first payment month = November 2026.

1. Combine the payments: M = $500 + $100 = $600 per month.
2. Convert APR to a monthly rate: r = 8 / 1200 = 0.0066667.
3. Calculate the months: n = ceil[−ln(1 − (0.0066667 × 20,000 / 600)) / ln(1.0066667)] = ceil(36.46) = 37 months.
4. Thirty-seven payments starting in November 2026 put the estimated final payment in November 2029 (displayed as 2029.11).
5. After 36 full payments, the estimated remaining balance is about $174.26. One month of interest adds about $1.16, so the final payment is approximately $175.42.

Assumptions

• The APR is fixed throughout the estimate.
• Payments occur monthly at the end of each period, with the first payment in the selected starting month.
• Interest compounds monthly at APR divided by 12.
• The regular and extra payments are applied to the loan balance; the extra amount is made every month.
• Fees, taxes, insurance, PMI, escrow, late charges, and lender-specific payment allocation are not included.

How Extra Payments Change Payoff Timing

Each payment first covers interest accrued for that period; what remains reduces principal. When an extra amount is applied to principal, the balance used to calculate later interest is smaller. That can shorten the repayment schedule and reduce interest over the life of the loan, assuming the rate and payment behavior match the model.

The timing and treatment of an extra payment matter. This calculator treats the extra amount as part of each monthly payment. A one-time lump sum, irregular extra amounts, or extra money sent on a different date will not follow this exact schedule. Some loan servicers may also require a specific instruction for additional funds to be applied to principal. Check the loan statement or servicing terms for how payments are credited.

Using and Interpreting the Estimate

Enter the current principal balance rather than the amount originally borrowed. Use the APR and payment amount that apply to the loan now, and enter the additional amount you expect to pay each month. Choose the month of the next scheduled payment as the first payment month. The output is an estimated count of payment periods and the month of the last payment—not a guaranteed date when the lender will show a zero balance.

For the example, the 37-month result means 36 full payments of $600 followed by an estimated smaller final payment. It does not mean the borrower makes 37 full $600 payments. The payoff date can shift if the next payment date changes, a payment is missed, or the lender applies interest differently.

Limits and Common Errors

• Payment too low: The regular payment plus extra must exceed the interest due each month. If it does not, the balance will not amortize under this formula, and the calculator cannot produce a finite payoff estimate.
• APR is not always the note rate: Enter the rate used to accrue interest on the balance. APR may include other costs in some loan disclosures, while this calculation treats the entered APR as the nominal annual interest rate.
• Balance changes: Use an up-to-date balance. A statement balance may differ from a payoff quote that includes interest accrued through a specific date or other amounts.
• Rounding: The month count rounds up to a whole payment period. The final payment is displayed to cents, so small differences can arise from lender rounding and the exact payment date.
• Changing rates or payments: Variable rates, payment holidays, skipped payments, and changing extra-payment amounts require a period-by-period schedule rather than this level-payment formula.

A frequent misconception is that adding $100 to a $500 payment necessarily cuts the payoff time by one-sixth. Interest accrues on the changing balance, so payoff timing is not generally proportional to the payment increase. The exact result depends on balance, rate, payment size, and when payments are credited.

Frequently Asked Questions

How do I calculate my loan payoff date with extra payments?
Use the current balance, monthly interest rate, regular payment, and extra amount. The formula estimates how many monthly periods are needed, then adds those periods to the month of the first payment.

Does an extra payment go directly to principal?
Not necessarily. The calculator assumes the extra amount reduces the loan balance after that period’s interest is covered. Confirm with the servicer how additional payments are credited.

Can I use this for a one-time extra payment?
This calculator models a fixed extra amount every month, not a single lump sum. A one-time payment needs a schedule that applies it in the month it is made and recalculates subsequent interest.

Why is my lender’s payoff date different?
The lender may use exact daily accrual, different payment-crediting dates, fees, a changing rate, or a different balance than the one entered. Request a current payoff figure for an exact amount and date.

What if my payment does not cover the monthly interest?
The balance will not be paid off under this fixed-payment model. Check the balance, APR, and payment amount; the calculator cannot estimate a finite payoff period when the payment does not exceed monthly interest.

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

Related

• Loan Calculator Based on Payment Amount: How Long to Pay It Off
• EMI Calculator: How the Monthly Instalment of a Loan Is Calculated
• Loan Calculator With Down Payment: Payment on What You Borrow

in bal | Remaining loan balance | $ | 20000 | 0.01 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in pmt | Regular monthly payment | $ | 500 | 0.01 | 100000000
in extra | Extra monthly payment | $ | 100 | 0 | 100000000
in yr | First payment year | - | 2026 | 1900 | 9999
in mo | First payment month | - | 11 | 1 | 12
out n | Months to payoff | months | ceil(round(-ln(1 - (apr / 1200) * bal / (pmt + extra)) / ln(1 + apr / 1200), 6)) | 0
out date | Estimated payoff month | - | yr + floor((mo - 1 + n - 1) / 12) + (mo - 1 + n - 1 - 12 * floor((mo - 1 + n - 1) / 12)) / 100 | 2
out final | Estimated final payment | $ | (bal * (1 + apr / 1200) ^ (n - 1) - (pmt + extra) * ((1 + apr / 1200) ^ (n - 1) - 1) / (apr / 1200)) * (1 + apr / 1200) | 2