Debt Avalanche Calculator
This page presets the avalanche strategy: each month's extra money targets the highest APR first. For the full side-by-side view of all three strategies, open the Debt Payoff Planner.
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Disclaimer
Not financial advice. This calculator is for educational purposes only and is not financial advice, tax advice, or a recommendation. Consider speaking with a qualified professional about your situation.
Assumptions. Interest is calculated monthly as balance × APR ÷ 12 and applied before each payment (monthly compounding). If you leave a minimum payment blank, it is estimated as the largest of: 2% of the balance, one month's interest + 1% of the balance, or $25 — actual minimums vary by lender. Simulations stop at 600 months. Displayed amounts are rounded to the nearest cent.
Data sources. Formulas: standard amortization math. No external data feeds. Page last updated: 2026-10-18.
How the math works
The debt avalanche is a payment ordering rule built around one observation: monthly interest equals balance times APR divided by 12, so each dollar sitting at a higher APR generates more interest than a dollar at a lower APR. Each month, after all minimums are covered, the remaining budget is aimed at the unpaid debt with the highest APR. Clearing the most expensive balances first is what minimizes the sum of interest across the plan at a fixed budget.
The ordering is recomputed every month from the balances carried into that month. Ties are broken by balance: equal APRs target the smaller balance first. If the target clears mid-month, the surplus cascades to the next unpaid debt in avalanche order, repeating until the month's budget is spent. Debts that reach zero drop out of the ordering entirely, and the engine's per-debt payoff months show the sequence the schedule followed.
Avalanche and snowball diverge only when the highest-APR debt is not the smallest balance. If one debt holds both titles, both orders aim at the same target every month and the results match; a single debt makes all four rows of the comparison table identical, which is the correct output rather than a bug. The comparison page runs both orders on your inputs so the difference is visible as numbers.
The underlying monthly loop is shared with every page on this site: interest first, then minimums — entered, or estimated as the largest of 2% of the balance, one month's interest plus 1% of the balance, or $25 when blank — then extras, then the remainder cascading down the priority order. Lump sums land on the current month's target first. When the budget falls short of total minimums, minimums are scaled proportionally and the shortfall is reported as a plain number.
The hybrid strategy with K set to 3 or more converges to pure avalanche when you start with K or fewer debts, since the switch condition is already met in month one. The snowball calculator runs the same engine with the smallest-balance-first order for contrast.
The simulation rests on four stated assumptions. One: interest compounds monthly — balance times APR divided by 12, applied before payments. Two: when a minimum is left blank it is estimated as the largest of 2% of the balance, one month's interest plus 1% of the balance, or $25, capped at the balance — an industry-typical approximation, not any lender's exact formula. Three: every simulation stops at 600 months, even if balances remain. Four: all internal math uses full double precision with no per-month rounding; displayed amounts are rounded half-up to the nearest cent after totals are computed.
One limitation to know: the engine uses the nominal APR divided by 12 as the monthly rate, which matches the standard US credit-card convention. Loans that accrue with a daily periodic rate produce slightly different month-to-month figures.
Worked example
Inputs: Debt A, balance $2,000, APR 24.99%, minimum $50 (entered); Debt B, balance $500, APR 12%, minimum $25 (entered); monthly budget $300. Avalanche targets A first (highest APR). Each month: interest first, then minimums ($50 to A, $25 to B), then the $225 remainder to A.
| Month | A interest | A paid | A end | B interest | B paid | B end |
|---|---|---|---|---|---|---|
| 1 | $41.65 | $275.00 | $1,766.65 | $5.00 | $25.00 | $480.00 |
| 2 | $36.79 | $275.00 | $1,528.44 | $4.80 | $25.00 | $459.80 |
Month 1: A interest $2,000 × 0.2499 ÷ 12 = $41.65, balance $2,041.65; B interest $500 × 0.12 ÷ 12 = $5.00, balance $505.00. Minimums leave A at $1,991.65 and B at $480.00; the $225 remainder goes to A, which ends at $1,766.65. Month 2: A interest $1,766.65 × 0.020825 = $36.7905, balance $1,803.4405; B interest $4.80, balance $484.80. After minimums and the $225 remainder, A ends at $1,528.4405, displayed $1,528.44, and B at $459.80. Under snowball on these same inputs, month 1's $225 would have gone to B (the smallest balance), leaving B at $255.00 instead of $480.00 — the same engine, a different target.
Frequently asked questions
What is the debt avalanche method?
It is a payoff ordering rule: each month, after all minimums are paid, any remaining budget goes to the unpaid debt with the highest APR. The ordering is recomputed monthly from the balances still owed, so as balances shrink the target can shift; cleared debts leave the ordering entirely.
Why does targeting the highest APR reduce total interest?
Monthly interest equals balance times APR divided by 12, so each dollar of balance at a higher APR accrues more interest than a dollar at a lower APR. Directing extra payments at the highest APR first shrinks the most expensive balances fastest, which lowers the sum of interest across the plan.
How are ties broken in the avalanche order?
Debts are sorted by APR from highest to lowest; when two APRs are equal, the smaller balance is targeted first. Any money left after the target clears cascades to the next unpaid debt in that same order until the month's budget is spent.
When does avalanche give the same result as snowball?
With a single debt both orders target the same balance, so every row of the comparison table matches. They can also match when the budget barely covers minimums, leaving almost no extra money to aim, or when the highest-APR debt is also the smallest balance.
What is the hybrid strategy's K setting?
Hybrid uses snowball order while more than K debts remain unpaid, then switches to avalanche order. K ranges from 1 to 10 with a default of 3. If K is greater than or equal to the number of debts, the plan runs in avalanche order from month one.
Do lump sums follow the avalanche order too?
Yes. A lump sum entered for a given month lands on that month's target debt first, then any remainder cascades down the current priority order. The schedule table shows the target debt receiving the lump sum and the following months reflecting the lower balance.