Enter a monthly budget and up to 20 credit cards to see how long the debt avalanche takes to clear them. You get the overall payoff time, total interest, a principal-versus-interest split, and a per-card schedule of payment phases.
Formula
Each month, interest is added to every remaining balance at the monthly rate, then payments are applied. Minimums are paid first; leftover budget goes to the highest APR, and leftover from a card that is paid off in that month cascades to the next-highest rate.
monthly rate r = APR / 12 / 100
interest this month = balance × r
new balance = balance + interest − payment
The number of months to clear a balance at a fixed payment is the usual
amortization inversion, n = −ln(1 − r × balance / payment) / ln(1 + r), but
with several cards the payment on each card changes whenever a higher-APR card
is retired, so this calculator walks month by month instead of using a single
closed form.
Raising the monthly budget shortens every card's schedule. Even a modest extra amount above the minimums cuts interest sharply because high-APR revolving balances compound every month.
Avalanche vs snowball
| Method | Extra payment goes to | Typical result |
|---|---|---|
| Avalanche (this calculator) | Highest interest rate | Lowest total interest |
| Snowball | Smallest remaining balance | Faster “wins,” usually more interest |
Examples
Three cards · $500 a month
Card 1 ($4,600 at 18.99%, $100 minimum), Card 2 ($3,900 at 19.99%, $90 minimum), and Card 3 ($6,000 at 15.99%, $120 minimum) take 38 months (3 years and 2 months) to clear on a $500 budget. Total payments are about $18,971, of which about $4,471 is interest. Avalanche order is Card 2, then Card 1, then Card 3.
Same cards · $700 a month
The same three cards on a $700 budget finish in 25 months (2 years and 1 month). Total payments drop to about $17,356 and interest to about $2,856 — roughly $1,600 less interest than the $500 plan, just from the extra $200 each month.