Snowball vs avalanche: pick your psychology
Both methods pay the same fixed monthly budget against the same debts. They differ only in which debt gets the surplus after minimums:
- Snowball attacks the smallest balance first. Debts die quickly and visibly, and every death frees a minimum payment that rolls onto the next target — the snowball grows.
- Avalanche attacks the highest interest rate first. It is mathematically optimal: total interest paid is as low as the budget allows.
The honest framing: avalanche wins every dollar-vs-dollar comparison, but debts are not retired by spreadsheets — they are retired by people who keep going. Research published in the Harvard Business Review and by Northwestern's Kellogg School found that "small victories" strategies increase people's sense of progress and their likelihood of completing payoff, which is why the calculator above defaults to snowball and makes the avalanche toggle one click away. The interest gap between the two on typical consumer debt loads is usually tens of dollars a year; the cost of quitting is the whole plan.
The engine's conventions, explained
Three rules run the simulation, and knowing them makes the verdict trustworthy:
- Interest first, at APR ÷ 12. Each month, every open debt accrues one twelfth of its annual rate on its current balance — the same convention card statements use. Then payments are applied.
- The budget never shrinks. Your monthly total (all minimums + extra) is fixed from month one. When a debt is paid off, its minimum does not return to your pocket — it cascades to the next target in strategy order. This rollover is the snowball effect itself, and it is why payoff timelines curve instead of run straight.
- Honest failure. If the budget can't even cover the interest on some debts, the calculator says the debt never clears instead of pretending. If minimums beat interest but the extra is zero, you still finish — just slowly.
A worked example
Three debts, minimums totaling $532/month, plus $200 of extra attack money:
- Credit card A: $9,000 at 22% APR, $180 minimum
- Credit card B: $2,400 at 19% APR, $72 minimum
- Car loan: $14,000 at 6.5% APR, $280 minimum
Run it: snowball (B first, then A, then car) clears everything in 44 months with $6,080 of total interest. Avalanche (A first) finishes one month sooner at $5,920 interest — a $160 edge, in exchange for your first closed account arriving months later. Now the part nobody believes until they run it: pay only the minimums and the same debts take 73 months and $13,332 of interest. The $200 extra saves $7,250 and nearly two and a half years. Extra dollars do the heavy lifting; ordering is a rounding-error optimization by comparison.
Reading your verdict
The headline gives your debt-free month and total interest for the current strategy; flip the toggle and both numbers update so the snowball-vs-avalanche decision is made on your balances, not a blog post's. When the last payment clears, redirect the entire freed budget — minimums plus extra — straight into investing, because a debt-free budget is a savings rate most people have never seen. The savings rate calculator will show what that new rate does to your retirement countdown.
Frequently asked questions
Is the snowball or avalanche method better?
Mathematically, avalanche — targeting the highest APR first — always pays the least interest. Behaviorally, research from the Harvard Business Review and Northwestern's Kellogg School finds people who pay off small balances first feel more progress and are more likely to finish, because closing accounts is the feedback loop that keeps the plan alive. Run both in the calculator above with your real numbers: the interest gap is usually smaller than people assume, and if it is, take the version you will actually complete.
How is monthly interest calculated?
Each debt's annual rate is divided by 12 and applied to the remaining balance every month — the same convention your card statements and most payoff calculators use. A 24% APR card accrues 2% of its balance each month. Some cards compound daily, which makes real balances marginally worse; at typical card rates the difference is a rounding error next to the order you pay debts in.
What happens to a debt's minimum payment after it is paid off?
It never leaves your budget — that is the snowball. When a debt closes, its freed minimum rolls onto the next target debt along with your extra payment, so the monthly attack amount only grows over time. This calculator holds the total budget fixed from day one: minimums plus extra, every month, until the last debt dies.
What if my minimums don't cover the interest?
The verdict will tell you the debt can never be paid off at this budget — balances grow faster than payments shrink them. That is not a verdict on you; it is arithmetic. Raise the monthly budget until the months figure appears, or talk to a nonprofit credit counselor before any for-profit 'relief' company.
How much extra should I pay each month?
As much as your budget tolerates, with one rule: the dollars doing the most guaranteed work are the ones attacking the highest APR. Paying down a 24% card is a guaranteed 24% return — no portfolio offers that. Keep a small cash buffer so an emergency doesn't re-grow the balances, then throw everything else at the debt until it's gone.
Related calculators
Convert the freed budget into a timeline with the savings rate calculator, see when the money can start working at Coast FIRE, or compare withdrawal assumptions on the 4 percent rule calculator — all on the FireVerdict hub.