The avalanche always costs less in interest; the snowball often wins in real life. The avalanche targets your highest-rate debt first, which is mathematically optimal. The snowball targets your smallest balance first, which delivers quick wins that keep you motivated. For most people, the dollar difference is smaller than they expect — so run your actual numbers, then pick the plan you'll actually follow.
What the two strategies actually do
Both strategies share the same skeleton, and the skeleton matters more than the difference between them. Every month you pay the minimum on every debt — never skip those — and then you throw your entire extra payment at one target debt. When that debt hits zero, its minimum payment joins the extra payment and the whole larger snowball rolls into the next target. That's why both plans accelerate: your monthly attack gets bigger with every debt you kill.
The only thing the strategies disagree on is which debt to target first:
- Snowball: target the smallest balance first, regardless of rate. You get your first "paid in full" the fastest, which is pure psychological fuel.
- Avalanche: target the highest APR first, regardless of balance. Every dollar of extra payment kills the most expensive interest first, which minimizes total interest paid.
Note what neither strategy does: spread the extra payment across all debts. Concentrating it is the whole trick — a focused $200 a month retires debts one by one, while $40 scattered across five debts barely dents any of them.
How the calculator simulates your payoff
The calculator doesn't use a shortcut formula — it simulates your payoff month by month, the way your balances actually evolve:
- Each debt accrues one month of interest: balance × APR ÷ 12.
- Minimum payments are applied to every debt.
- The full extra payment goes to the current target debt (smallest balance for snowball, highest APR for avalanche). If the extra payment finishes a debt, the remainder cascades to the next target.
- The month a debt reaches zero, its minimum payment is added to the attack on the next target.
The simulation assumes fixed APRs, no new purchases, and no late fees. It caps at 100 years — if a debt can't be paid off because its minimum doesn't even cover the monthly interest, the calculator tells you plainly instead of pretending.
Worked example
Jordan has three debts and an extra $200/month:
- Store card: $1,800 at 24.99% APR, $50 minimum
- Visa: $6,500 at 19.99% APR, $150 minimum
- Personal loan: $4,200 at 11.99% APR, $120 minimum
Snowball targets the $1,800 store card first (smallest balance), then the $4,200 loan, then the Visa. Avalanche targets the store card first too — because 24.99% is also the highest rate — then the Visa, then the loan. In Jordan's case the two strategies start identically and only diverge on the second target.
The simulation shows the avalanche finishing a couple of months sooner and saving a few hundred dollars in interest — real money, but not life-changing. Jordan picks the snowball anyway, because he knows himself: he needs the early wins. That self-knowledge is worth more than the interest difference.
The honest answer to "which is better?"
Personal finance forums treat this as a holy war, but the research and the math agree on something boring: the best strategy is the one you finish. Studies on debt repayment consistently find that people who focus on small balances first are more likely to become debt-free — not because the math is better, but because early progress builds momentum, and momentum is what survives month nine of a two-year plan.
That said, don't romanticize the snowball past the point of reason. If your highest-rate debt is enormous and your smallest balance is trivial, the avalanche's savings can be substantial — run the numbers above and look at the actual dollar gap before deciding. A $2,000 interest difference is a real argument for discipline. A $150 difference is permission to choose motivation.
One more thing the debate usually misses: the extra payment amount matters far more than the strategy. Going from $0 extra to $200 extra typically saves years and thousands of dollars. Going from snowball to avalanche typically saves months and hundreds. If you take one action from this page, make it finding an extra payment — any extra payment — not perfecting the order.