Loan Payoff Calculator
Find out when your loan actually ends — and how much sooner it could end if you paid a little extra each month. The calculator runs both timelines side by side so you can see exactly what an extra $20, $50 or $100 is worth.
How the payoff calculation works
There is no formula for "when does this end" when you pay a flat amount — it has to be walked forward month by month. That is exactly what happens above, twice:
- Charge interest on the current balance (balance × APR ÷ 12).
- Subtract your payment (plus any extra).
- Carry the remainder into next month. Repeat until it hits zero.
Counting the loops gives your payoff date. Adding up step one gives the total interest. Running the whole thing twice — with and without the extra — gives the difference in green.
Why $100 buys 18 months
Your normal payment is mostly interest at the start. An extra payment is different: it is 100% principal. It skips the interest queue entirely and deletes balance directly.
And deleted balance never comes back. A dollar removed in month one is a dollar that never gets charged interest again — for all 55 remaining months. That is why $100 a month turns into $1,605 of savings: it is not $100 of relief, it is $100 compounding against you in reverse.
The asymmetry that matters
An extra dollar in month one dodges interest 55 times. The same dollar in the final month dodges it once. If you are going to pay extra at all, the single best month to start is this one — not after the bonus, not next year.
$12,000 at 15%, with and without $100
The default numbers above, laid out in full.
| Paying $300 | Paying $400 | |
|---|---|---|
| Balance | $12,000 | $12,000 |
| APR | 15% | 15% |
| Payoff time | 56 months | 38 months |
| Interest paid | $4,739.59 | $3,134.26 |
| Total repaid | $16,739.59 | $15,134.26 |
You put in an extra $3,800 over the life of the loan ($100 × 38 months) and you get back $1,605.33 in interest you never pay — plus you are free 18 months earlier. That is roughly a 42% return on the extra money, guaranteed, tax-free, and it is available to anyone with a spare $100.
Try dropping the extra to $25 in the calculator. It still moves the needle far more than most people assume.
When not to rush the payoff
Paying extra is usually right — but not always first.
- No emergency fund yet. Clear a small buffer first, or the next broken transmission puts you straight back into borrowing at a worse rate.
- A more expensive debt exists. Extra money belongs on the highest rate you owe. Compare with the debt payoff calculator.
- There is a prepayment penalty. Rare on personal loans, but check — it can cancel the saving.
- A lower rate is available. If you can refinance or consolidate below your current APR, that beats paying extra at the old rate. See the consolidation calculator.
If none of those apply, the extra payment is one of the highest-certainty returns in personal finance — and it starts working the month you begin.
Loan payoff calculator FAQ
How does a loan payoff calculator work?
It walks forward month by month: charge interest on the balance, subtract your payment, carry the rest into next month, repeat until zero. Counting the months gives the payoff date; summing the interest gives the cost. Running it twice — with and without extra — shows the difference.
How much does paying extra actually save?
On $12,000 at 15%, paying $300/month takes 56 months and $4,739.59 in interest. Adding $100/month cuts it to 38 months and $3,134.26 — saving $1,605.33 and 18 months.
Why does an extra payment save so much?
Interest is charged on what you still owe, so an extra dollar today removes a dollar of balance for every remaining month — dodging interest again and again. The same dollar paid at the end dodges it once. Early extra payments are worth far more.
Will my lender charge a penalty for paying early?
Most personal and installment loans have no prepayment penalty. Some lenders do, and a few apply extra money to future scheduled payments instead of principal — which kills the benefit. Check your agreement and instruct them in writing.
Should I pay off the loan early or save the money?
Compare the rate. Paying off a 15–36% loan is a guaranteed return equal to that rate, which savings accounts cannot match, so high-rate debt usually wins. The exception is a small emergency fund — keep a buffer first.
Does paying off a loan early hurt my credit?
It may cause a small, temporary dip since an active installment account closes and stops adding on-time payments. The effect is minor and short-lived; the interest saved is almost always worth more.
What if my payment does not cover the interest?
Then the balance grows and the loan never ends. The calculator flags this. You need a different plan — consolidating to a lower rate, or a hardship arrangement with the lender.
A lower rate beats a bigger payment.
Paying extra fights the interest. A lower APR removes it. Check what you qualify for in about 5 minutes — soft check, no impact to your credit.
Related tools & guides
- Debt payoff calculator — snowball vs avalanche across several debts.
- Amortization calculator — the full month-by-month schedule.
- Debt consolidation calculator — what a lower rate would save.
- Is debt consolidation a good idea? — when it beats paying extra.