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When will this loan be gone?
On the defaults — $18,000 at 9.99% with $350/month — the loan takes about 68 months with roughly $5,600 in interest. Adding $100/month cuts about 19 months and $1,600. Enter your numbers.
FREE TOOL · MONEY
Loan Payoff Calculator
Enter your balance, APR, and monthly payment to see your payoff date and total interest — and exactly how much an extra payment each month saves you, in dollars and in months off the loan.
The extra-payment math, in one paragraph
Every loan payment splits into interest first, principal second: the lender takes its cut (balance × monthly rate), and whatever is left shrinks what you owe. An extra payment skips the line entirely — it goes straight to principal, which means every future payment accrues interest on a smaller balance. That is why $100 extra a month does not just shave $100 off the timeline; it compounds in reverse, erasing thousands in interest you would otherwise have paid.
A worked example
Take an $18,000 balance at 9.99% APR with a $350/month payment. The monthly rate is 9.99% ÷ 12 = 0.8325%, so month one accrues $18,000 × 0.008325 = $149.85 in interest — only $200.15 touches the principal. Run the amortization out and the loan takes about 68 months with roughly $5,600 in total interest. Add $100 extra a month ($450 total): the payoff drops to about 49 months and total interest to about $4,000 — saving roughly $1,600 and 19 months. The calculator above replays this exact math on your numbers, including your debt-free month.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Months to payoff | −ln(1 − r·B÷P) ÷ ln(1+r) | r = APR÷12, B = balance, P = payment. The exact amortization solution. |
| Total interest | months × payment − balance | Everything you pay above what you borrowed. |
| Interest saved | interest(base) − interest(extra) | Dollars the extra payment keeps in your pocket. |
| Debt-free date | today + months | The calendar month the balance hits zero. |
The minimum-payment trap
If your payment barely covers the monthly interest, the loan barely moves: on the example above, a $160 payment against $149.85 of interest retires only $10.15 of principal a month — a 15-year sentence on an $18,000 loan, with interest nearly doubling what you borrowed. The calculator refuses payments that cannot clear the interest and tells you the floor instead. The fix is never mysterious: raise the payment, or refinance the rate.
Who uses this
- Anyone with a car loan or personal loan: the payoff date turns an abstract balance into a finish line.
- Debt-payoff planners: compare the avalanche target against this page, then pick the highest-rate loan to feed extra payments.
- Refinance shoppers: run the current loan here first, so a new offer has something concrete to beat.
- Budget builders: the monthly-interest figure is the true cost of carrying the debt one more month.
Accuracy & limitations
The math is exact for fixed-rate, fixed-payment loans (personal loans, auto loans, standard mortgages) with no fees and no prepayment penalty. It does not model variable rates, interest-only periods, balloon payments, or loans where interest accrues daily with a different day-count convention — those can shift the payoff by a month or two. A few lenders charge prepayment penalties; check your note before sending extra. Figures are estimates for planning, not loan advice.
Planning the attack order? The snowball vs avalanche calculator picks which loan gets the extra payment, and the extra loan payment calculator sizes it. The method behind choosing is in the comparison library.
Cite this calculatorBright Side Kit. “Loan Payoff Calculator.” brightoolbox.com, 2026.
Bright Side Kit. "Loan Payoff Calculator." https://brightoolbox.com/loan-payoff-calculator/ Accessed October 22, 2026.Frequently asked questions
How is the payoff date calculated?
From the amortization formula: months = −ln(1 − r·B÷P) ÷ ln(1+r), where r is the monthly rate, B the balance, and P the payment. The calculator rounds up to whole months and adds them to today. Try it on the loan payoff calculator above.
Why does an extra $100 save more than $100 a month of time?
Because extra payments skip the interest queue and hit principal directly. A smaller balance means less interest next month, which means more of the regular payment hits principal too — the effect compounds in reverse for the rest of the loan.
What if my payment barely covers the interest?
Then the loan is nearly frozen: almost every dollar goes to the lender and almost nothing retires the balance. The calculator flags this and shows the minimum payment that actually moves the needle. The escape is a bigger payment, a lower rate, or both.
Does paying extra reduce the monthly payment?
No — the scheduled payment stays the same; the loan just ends sooner. (A mortgage recast is the exception: a lump sum plus a small fee re-amortizes the loan to a lower payment. See recast vs refinance.)
Should I pay extra on the loan or invest the money?
Compare the loan's APR against your expected after-tax investment return, adjusted for risk. Paying down a 10% loan is a guaranteed 10% return; investing is a hoped-for one. The pay off debt vs invest calculator runs your exact numbers.
Do extra payments trigger prepayment penalties?
Rarely on personal and auto loans, sometimes on mortgages — check your promissory note for a prepayment clause before sending extra. Most modern consumer loans have no penalty at all.
Why doesn't my lender's payoff quote match this?
Payoff quotes add per-diem interest through the payoff date plus any fees, and daily-accrual loans differ slightly from monthly math. Expect a difference of days of interest, not months.