How this is calculated
- Your monthly attack budget. Every month you pay the same total:
budget = sum of all minimum payments + extra payment. The budget never shrinks — that's the debt-rollover method. When a debt is finished, its minimum doesn't go back in your pocket; it joins the extra payment and rolls into the next target. That snowballing of freed-up minimums is what makes both strategies fast. - Interest, month by month. Each simulated month, every open debt first
accrues interest on its remaining balance:
interest = balance × APR ÷ 12. Then every open debt receives its minimum payment, and the leftover budget (extra + freed-up minimums) all goes to the target debt. If the target is finished mid-month, the remainder cascades to the next target the same month. - The only difference between the strategies is the target. Avalanche targets the highest APR (ties broken by smaller balance); snowball targets the smallest balance (ties broken by higher APR). Avalanche is mathematically optimal: every extra dollar retires the most-expensive principal first, so total interest is always the minimum possible and the payoff date is never later than snowball's. Snowball wins on behavior — studies of real borrowers (including Kellogg School research on "small victories") find that closing whole accounts early keeps people paying extra, and a plan you stick with beats a plan you abandon. The verdict box above prices that trade-off for your exact debts.
- The extra-payment lever. To price what your one extra payment is
worth, the planner also runs the same avalanche plan with the extra set to
$0— the minimums-only baseline — and reports the gap in the green box: how many months sooner you reach zero and how much interest you never pay. Because that extra dollar retires principal that would otherwise keep compounding — and each finished debt's freed-up minimum rolls onto the next target — the savings grow non-linearly, so the first slice of extra usually buys the biggest jump. - Guard rails. If a debt's monthly interest is at least as large as its minimum payment, the minimum can never retire it — the planner flags that debt instead of pretending. The simulation also hard-stops at 600 months (50 years) and tells you if the plan never finishes.
What this doesn't model: daily compounding on average daily balance (real card interest runs slightly different from the monthly model), promotional/deferred rates, variable APR changes, new spending on the cards, late fees, or minimums that shrink as the balance falls (we hold minimums fixed, which is what most payoff plans assume — keep paying the original minimum). It's a planning estimate, not a statement schedule.
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Debt Avalanche vs Snowball Which method clears your debt faster — and which one you'll actually stick with.Frequently asked questions
Which is better, debt avalanche or debt snowball?
Mathematically, the avalanche method (paying extra toward the highest-APR debt first) always finishes with the least total interest and never later than snowball. But research on real borrowers finds the snowball method (smallest balance first) produces quick early wins that help people stick with the plan. This planner shows the exact dollar-and-month gap between the two on your debts, so you can decide whether the avalanche savings are worth more to you than the snowball momentum.
Should I include my mortgage in a debt payoff plan?
Usually no. Avalanche and snowball plans are designed for consumer debts — credit cards, car loans, personal loans, student loans. Mortgages have low rates, very long terms, and potential tax treatment that make them a separate decision; adding a 30-year mortgage would also dominate the chart and hide your real progress. Most planners recommend attacking consumer debt first, then deciding separately whether to prepay the mortgage or invest.
What if I can't afford the minimum payments on my debts?
Neither avalanche nor snowball works until every minimum is covered — this planner will warn you when a debt's monthly interest is as large as its minimum payment, because such a debt never pays off. If you're in that spot, options include calling the lender for a hardship plan, a nonprofit credit-counseling agency's debt-management plan, consolidating at a lower rate, or a 0% balance transfer. Talk to a qualified counselor; this tool is an estimator, not advice.
How is the interest on each debt calculated?
Each simulated month, every open debt accrues interest equal to its remaining balance times APR divided by 12 (the monthly periodic rate). Payments are then applied: the minimum on every debt, with the extra payment plus any freed-up minimums from already-paid-off debts going to the target debt. Real card issuers compound daily on average daily balance, so real totals will differ slightly — the monthly model is the standard planning approximation.
How much does an extra $100/month save?
More than most people expect, because the effect compounds: every extra dollar retires principal that would otherwise keep accruing interest, and once a debt is gone its old minimum rolls onto the next one. On the three starter debts loaded above, raising the extra payment from $0 to $100/month clears the plan about 17 months sooner and saves roughly $5,400 in interest (avalanche); a $200/month extra roughly doubles that to about 26 months and $7,600. Your own numbers will differ — enter them and watch the green "extra-payment lever" box update. Because the savings are non-linear, the first $100 usually buys the biggest jump, with later increases helping less per dollar.
Does this planner store or send my debt information?
No. Everything runs in your browser and nothing you type is sent to a server. The "copy shareable link" button encodes your debts into the link itself, so only people you share that link with can see them.
This planner is an educational estimate, not financial advice, not credit counseling, and not a debt-relief offer. Real interest accrual, fees, and minimum payments vary by lender; verify your plan against your statements or with a qualified counselor. No liability is accepted for decisions made from these results.