How this snowball vs. avalanche calculator works
When you owe money in several places, the question is not only how much to pay but where each extra dollar should go. This calculator takes one total monthly budget and runs your debts through two well-known payoff orders, month by month, until every balance is zero. Both runs use the same balances, the same rates and the same budget, so the only difference you see is the order.
Every month, the simulation adds interest to each open balance, pays every required minimum, and then sends whatever is left of the budget to the current target. When the target is paid off, the money that was going to it, including its old minimum, rolls straight into the next target in the same month. That rollover is what makes both methods accelerate over time.
Snowball vs. avalanche in one minute
| Debt snowball | Debt avalanche | |
|---|---|---|
| Target first | Smallest balance | Highest APR |
| Total interest | Same or higher | Same or lower |
| First payoff | Usually sooner | Can take many months |
| Best for | People who need early momentum | People motivated by the total cost |
The avalanche is the mathematically optimal order for minimizing interest when every debt has a fixed rate and you have a fixed budget. The snowball trades some interest for faster, visible progress. Neither one changes how much you owe; they only change how long the expensive part of it survives.
The math behind each month
For every debt i in month t, interest is the monthly periodic rate times the opening balance:
The extra money available for the target is the budget minus every minimum still owed:
As debts disappear, their minimums drop out of the sum and E grows. The target is the open debt with the lowest balance (snowball) or the highest APR (avalanche); ties are broken by the other rule.
Because interest is proportional to rate times balance, every dollar that retires a 27% balance saves more than a dollar that retires an 8% balance. That is the entire case for the avalanche in one line.
Worked example: four debts, $1,000 a month
The default scenario above is a realistic mix of revolving and installment debt:
| Debt | Balance | APR | Minimum |
|---|---|---|---|
| Store card | $1,200 | 21.99% | $40 |
| Visa card | $6,800 | 27.49% | $204 |
| Personal loan | $4,000 | 13.5% | $136 |
| Auto loan | $9,500 | 7.9% | $290 |
| Total | $21,500 | $670 |
With a $1,000 budget, $330 a month is free to accelerate. The snowball attacks the Store card first and clears it in month 4. The avalanche goes after the Visa card at 27.49% and does not close its first account until month 16.
By the end, the avalanche finishes in 2 yr 1 mo with $3,366.61 of interest. The snowball takes 2 yr 2 mo and $3,891.13. The avalanche saves $524.52; the snowball buys you a first win 12 months earlier.
Why the size of your budget matters more than the order
The order is worth a few hundred dollars in this example. The budget is worth thousands. Here is the same set of debts under different monthly budgets, using the avalanche:
| Monthly budget | Debt-free in | Total interest |
|---|---|---|
| $670 (minimums only) | 3 yr 8 mo | $7,819 |
| $800 | 2 yr 10 mo | $5,015 |
| $1,000 | 2 yr 1 mo | $3,367 |
| $1,500 | 1 yr 4 mo | $1,965 |
The lesson: decide on the biggest monthly amount you can protect first, then pick the order. Even a small, permanent increase compounds, because each extra dollar removes interest that would otherwise be charged every month for the rest of the plan.
How to choose between snowball and avalanche
- Run your own numbers. If the interest difference above is small, the snowball’s faster wins may be worth it. If it is large, the avalanche is the better deal.
- Look at the rate spread. When your rates are close together, the order barely matters. When one card is far above the rest, the avalanche pulls ahead quickly.
- Be honest about motivation. If you have started and stopped a payoff plan before, an early win can be the difference between finishing and quitting.
- Try a hybrid. Some people clear one or two tiny balances first for momentum, then switch to the avalanche for everything else.
- Protect the plan. Automate the minimums, schedule the extra payment right after payday, and stop adding new charges to the cards you are paying down.
If a single card dominates your debt, the credit card payoff calculator shows how much a higher fixed payment saves on that card alone. For installment loans in the list, the loan amortization calculator shows what extra principal does to a fixed term.
Assumptions and limits
- Rates are fixed, interest is calculated monthly at APR ÷ 12, and payments land at the end of each month.
- Minimums stay at the dollar amount you enter. Real card minimums usually fall as balances fall; installment loan payments do not.
- No new charges, fees, promotional rates or missed payments are included.
- The budget stays the same every month, and freed-up minimums roll into the next target immediately.