Debt Snowball &
Avalanche Calculator

Both pay minimums on every debt and aim all extra money at one debt at a time. The snowball method targets the smallest balance first, so you get quick wins and motivation. The avalanche method targets the highest interest rate first, so you pay the least total interest overall. This calculator runs both and shows you the exact difference in months and dollars for your debts.

It runs a month-by-month simulation: each month, interest accrues on every balance at APR/12, minimums are paid, and the remaining payment pool (minimums freed up by paid-off debts plus any extra you add) is swept onto the target debt. When a balance hits zero, its minimum payment rolls into the pool. The result is a realistic payoff schedule rather than a rough estimate.

No. The entire simulation runs in your browser with plain JavaScript. Your debts, balances, and plan are never uploaded, stored on a server, or transmitted anywhere. The calculator even works offline after the page loads, and your entries auto-save locally so you don't lose them between visits.

Avalanche costs less in total interest and finishes sooner on paper, but snowball is easier to stick with because you see debts disappear faster. If your balances are close in size, avalanche's interest advantage is small and snowball's motivation wins. If one debt has a much higher rate, avalanche usually wins big. The chart and comparison panel show the tradeoff for your exact numbers.

Yes. Add any extra amount you can put toward debt each month and it is included in the payment pool immediately, speeding up every payoff date. You can compare the same debts with and without the extra to see exactly how much time and interest it saves.

If a minimum payment is below the monthly interest on that balance, the balance grows instead of shrinking — the simulation will show that debt as 'underwater'. That's a real red flag worth seeing: bump the payment or tackle that debt first. The calculator marks such debts clearly so nothing is hidden.