Debt payoff calculator
Enter a balance, its APR, and what you can pay each month. The calculator walks the balance down month by month and returns the payoff date, the total interest, and exactly what an extra payment buys you.
Your payoff plan
One balance, one fixed monthly payment, walked down month by month.
How the payoff math works
Interest is charged on whatever balance remains, so a payment does two jobs at once: part covers that month’s interest, and the rest reduces the balance. Early on, when the balance is largest, interest takes the biggest share — which is why a balance feels stuck for months and then suddenly starts falling. This calculator reproduces that process exactly: each month it adds interest at one-twelfth of the APR, subtracts your payment, and repeats until the balance reaches zero. The last payment is smaller than the others, because only the remaining balance plus one month of interest is owed.
A $5,000 balance at 24% APR, paid at $200 a month, takes 36 months and costs $2,001 in interest. Add $100 extra every month and the same balance clears in 21 months at $1,143 of interest — $857 saved, and the debt gone 15 months sooner. The extra payment does not change the APR; it shrinks the balance that interest is charged on.
Avalanche vs. snowball
With several debts, the order matters. The avalanche method pays minimums on everything and sends every spare dollar to the highest APR — it always produces the lowest total interest. The snowball method clears the smallest balance first; it costs more interest, but the early wins keep some people paying when the avalanche’s slower visible progress would not. For a single balance the two methods are the same plan, which is why this calculator models one balance at a time: run each debt, note its interest rate, and the avalanche order is simply highest APR first.
Where the extra payment comes from
Extra principal has to come from somewhere real. Three sources this site covers elsewhere: withholding tuned with a W-4 adjustment can free a monthly amount that was previously waiting for a refund; the 50-30-20 budget calculator shows which spending line can give up a fixed monthly slice; and a tax refund applied as a lump sum works like several extra payments arriving at once — enter it as a few months of extra payments to approximate the effect. What matters is that the source repeats. A heroic payment in January followed by minimums all year saves far less than a modest extra that never misses.
Choose the payment you can sustain for the entire payoff, not the largest one you can survive for two months. A plan that survives a bad month beats an aggressive plan abandoned in month three.
Frequently asked questions
How does this calculator find my payoff date?
It simulates the balance month by month: each month it adds interest at one-twelfth of the APR, subtracts your payment, and repeats until the balance reaches zero. The final payment is smaller than the rest, which is why payoff dates rarely land on a round number of years.
What happens if my payment is smaller than the monthly interest?
The balance never falls — each payment is absorbed by interest and the debt can even grow. The calculator flags this case instead of inventing a date. Any payment above the first month’s interest will eventually clear the balance, though slowly at first.
Which is better, the avalanche or the snowball method?
Avalanche — paying the highest APR first — always costs the least interest. Snowball — clearing the smallest balance first — costs more but gives earlier wins, which helps some people stick with the plan. With a single balance the two are identical; the choice only matters across several debts.
Should extra money go to debt or to investing?
Paying off a 24% APR balance earns a guaranteed 24% return; no investment promises that. A common order is: capture any employer retirement match, clear high-APR debt, then invest. Low-APR debt, like an inexpensive mortgage, is where the comparison genuinely gets close.
Does this work for a mortgage, car loan, or student loan?
Yes — any fixed-rate balance paid monthly. It does not model variable rates, new charges on the account, fees, or prepayment penalties, so check those terms before sending extra principal.