Debt Payoff Calculator: Avalanche vs Snowball
Enter your debts and extra monthly payment — see both payoff methods side by side: months to debt-free and total interest paid under each.
Free, no signup, runs entirely in your browser — nothing you type is sent anywhere. Estimates for planning, not financial advice.
How this calculator works
It runs a month-by-month simulation of both payoff methods on your actual debts. Each month: interest accrues on every balance at APR/12, minimum payments apply to all debts, and your extra payment goes to the target debt — highest APR first (avalanche) or smallest balance first (snowball). When a debt closes, its minimum payment rolls into the pool, which is what makes both methods accelerate over time.
Avalanche always wins mathematically — usually by hundreds to a few thousand dollars on typical debt loads. But a 2016 study from Northwestern's Kellogg School (Brown & Lahey) found snowball payers retire more total debt in practice, because closing accounts early keeps people in the game. The calculator shows both so you can see the real price of the motivation: if the interest difference is small, take the snowball wins guilt-free.
Two rules that matter more than the method
First, keep a $500-$1,000 starter emergency fund before going hard on extra payments — otherwise the next surprise lands back on the card and undoes a month of progress. Second, the extra-payment number is the entire engine: at typical balances, an extra $100/month often cuts years off the timeline. Find it in subscription audits and food-delivery markups before touching groceries.
Common questions
Which method should I actually pick?
Run both above and look at the interest difference. If avalanche saves you less than a few hundred dollars, pick snowball — the early account closures are worth more as motivation than the interest as math. If the difference is large (common when a high-APR card has a big balance), avalanche. The only wrong choice is switching methods every month; pick one and run it for at least 12 months.
Why does the calculator override very low minimum payments?
If a minimum payment doesn't cover the monthly interest, the balance grows forever and the simulation never ends — which is also true in real life. The calculator floors each minimum at interest-plus-$5 so the math terminates. If your real minimum is below your monthly interest accrual, that debt is in negative amortization and needs to be the immediate priority regardless of method.
Should I pay off debt or invest?
Compare interest rates to realistic returns. Credit cards at 20-25% APR beat any reliable investment — pay them first, always. Debt at 6-8% (many student and car loans) is roughly at the long-run equity return boundary; either choice is defensible, so the tiebreakers are your risk tolerance and whether you have an employer 401(k) match (capture the match first — it's an instant 50-100% return). Debt under 4-5%: minimums only, invest the difference.
Does this account for new spending on the cards?
No — it assumes the balances only go down. That assumption is the whole game: a payoff plan with continued card spending is a treadmill. The standard fix is moving day-to-day spending to debit or cash while the payoff runs, and keeping a starter emergency fund so surprises don't force the card back out. Track spending by category weekly so drift shows up in days, not statements.
Put the number to work in Cash Compass
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