Transparent method
The formula
Worked example
Example inputs
How to interpret the result
An extra payment applied consistently doesn't just shave a proportional sliver off the payoff timeline. Because interest is calculated on a shrinking balance, an extra payment made early in the loan removes more future interest than the identical extra payment made later, so timing the extra payment earlier compounds its benefit.
Before you rely on it
What to check
Compare payoff time and total interest saved at a few different extra-payment amounts, since the relationship between extra payment size and time saved isn't a straight line.
The common error
Where people go wrong with loan payoff calculator
Assuming a modest extra monthly payment only shaves a proportionally modest amount off the loan term. Because it comes straight off principal early, its effect on total interest paid is often larger than a quick mental estimate suggests.
Sensitivity evidence
How annual interest rate changes the months to payoff
| Annual interest rate | Months to payoff | Remaining interest |
|---|---|---|
| 4.5% | 43.4 months | $1,539 |
| 6.5% | 45.2 months | $2,342 |
| 8.5%worked example | 47.2 months | $3,239 |
| 10.5% | 49.4 months | $4,251 |
| 12.5% | 52.0 months | $5,406 |
Every input, tested
Which input moves the months to payoff most
| Input | Tested from | To | Months to payoff at each end | Swing |
|---|---|---|---|---|
| Monthly payment | $405 | $495 | 53.6 months to 42.2 months | 11.4 months (24%) |
| Current balance | $16,200 | $19,800 | 41.7 months to 52.9 months | 11.2 months (24%) |
| Annual interest rate | 6.5% | 10.5% | 45.2 months to 49.4 months | 4.2 months (9.0%) |
Two variables at once
Months to payoff by annual interest rate and current balance
| Annual interest rate \ Current balance | $14,400 | $18,000 | $21,600 |
|---|---|---|---|
| 4.5% | 34.2 months | 43.4 months | 53.0 months |
| 6.5% | 35.2 months | 45.2 months | 55.7 months |
| 8.5% | 36.4 months | 47.2 months | 58.9 months |
| 10.5% | 37.7 months | 49.4 months | 62.5 months |
| 12.5% | 39.1 months | 52.0 months | 66.9 months |
Step by step
The worked example, input by input
| Input | Value used |
|---|---|
| Current balance | $18,000 |
| Annual interest rate | 8.5% |
| Monthly payment | $450 |
| Months to payoff | 47.2 months |
| Remaining interest | $3,239 |
Where the inputs come from
Use the current principal balance from the latest statement or the lender's payoff quote, not the original loan amount. The payment is the amount you actually send each month, which may be higher than the required minimum if you already pay extra. The rate is the annual note rate. If your statement lists a payoff figure that includes accrued interest, that number can differ slightly from the balance you enter here.
When the result stops applying
The estimate holds only while the payment and rate stay constant and the lender applies the extra to principal. Some lenders treat surplus as an early payment on next month's bill instead, which saves no interest until you tell them to apply it to principal. Loans with a prepayment penalty, a variable rate or precomputed interest will not follow this curve.
What to compare it with
Use the payoff estimate together with the amortization schedule to see how much of the next payment is interest. If you carry several debts, the debt avalanche and snowball calculators show which balance to attack first, and the highest rate usually wins. Before sending extra money, check that you have an emergency fund and that no cheaper source of cash exists. The best target for a spare hundred dollars is the loan with the highest rate and no prepayment charge, not necessarily the one with the largest balance.
People also ask
Frequently asked questions
Why does the payoff take longer than the balance divided by the payment?
Part of every payment covers interest, so principal falls more slowly than the payment suggests. Dividing balance by payment ignores interest and always understates the time.
Does paying extra always help?
It always lowers interest on an interest-bearing loan, but the value depends on the rate. Extra payments on a 3% loan may be better used against a 20% card balance.
How do I make sure extra money goes to principal?
Write "apply to principal" on the payment or use the lender's extra-principal option online, then check the next statement to see the balance fell by the extra amount.