About this calculator
One card is easy to plan for; real life is three cards, a store card and a loan, each with its own APR and minimum. This planner simulates all of them together, month by month, under a single fixed budget: every minimum gets paid, everything left over attacks one target debt, and when a debt dies its minimum rolls into the next target — the rollover is where both famous strategies get their power.
The two strategies differ only in target order. Avalanche aims at the highest APR first and is always the cheapest in interest. Snowball aims at the smallest balance first, costs a little more, but produces early wins that research links to better follow-through. The planner runs both on your numbers and shows the exact dollar difference, so the choice is yours with the price tag attached.
How to use it
- List each debt’s balance, APR and minimum payment from your statements (leave unused rows at zero).
- Add any extra you can pay each month on top of the minimums.
- Pick a strategy — then flip it to see the comparison line and how the payoff order changes.
The formula
Your total monthly outlay never changes: sum of minimums plus your extra. As debts clear, their minimums join the attack on the next target, which is why the last debts fall so much faster than the first.
Worked example
Two cards — $6,500 at 24.99% (minimum $130) and $3,200 at 19.99% (minimum $75) — plus $200 extra a month, a $405 total budget. Avalanche clears the expensive card in month 26 and the second card in month 33: debt-free by July 2029 with $3,351 of interest. Snowball takes a month longer and costs $346 more, because the expensive card waits its turn. Drop the extra to zero and the same two cards take 144 months — twelve years — and $19,767 of interest, because the big card’s $130 minimum does not even cover its first month of interest ($135).
Sources: Standard amortization simulation with payment rollover; strategy comparison follows the published snowball-versus-avalanche literature. Last updated: October 2026.
Frequently asked questions
Snowball or avalanche: which is actually better?
Mathematically, avalanche never costs more interest — sometimes only a few dollars more, sometimes thousands. Behaviourally, studies (notably Kellogg School research on small victories) find people who clear small balances first are more likely to eliminate their overall debt. The planner shows both interest totals on your debts: if the gap is small, take the motivation; if it is large, take the savings.
Why does the plan keep my payment fixed when a debt clears?
That rollover is the engine of both methods. If you pocket the freed minimum instead, the plan still works but stretches out and costs more interest. Keeping the total constant means every cleared debt accelerates the next one — the final debt gets your entire budget thrown at it.
What if my minimum does not cover the monthly interest?
Then that balance grows even while you pay — it happens with very low minimums on high-APR cards. The planner flags any plan whose total payments cannot cover the first month’s interest, because such a plan never finishes. Raising the extra payment, or calling the issuer about a hardship APR, changes the math.
Should I include my mortgage or car loan?
You can — any fixed debt with a balance, a rate and a monthly payment fits the model. Most people run cards and personal loans here, because mortgage and car rates are low enough that extra payments usually earn more elsewhere (and mortgage interest may be deductible). Including them still shows a truthful payoff date.
What formula does this debt payoff planner calculator use?
Monthly: interest accrues at APR ÷ 12 on each balance; minimums are paid on all debts; the remaining budget goes to the target (avalanche: highest APR, snowball: lowest balance) until it clears, then rolls on. Your total monthly outlay never changes: sum of minimums plus your extra. As debts clear, their minimums join the attack on the next target, which is why the last debts fall so much faster than the first. The worked example on this page applies the formula step by step with real numbers, so you can verify the result by hand.