How both strategies work
You pay minimums on everything and aim all extra money at one target debt. When it's gone, its payment rolls into the next target — the "snowball" that grows as each debt falls. The only difference is targeting: snowball orders by smallest balance for fast psychological wins; avalanche orders by highest interest rate for mathematical efficiency.
Which one should you pick?
Avalanche always wins on paper — it can't lose, because it kills the most expensive debt first. But the margin is often smaller than expected (frequently a few hundred dollars over the whole payoff), while research on debt repayment consistently finds people who see quick early wins are more likely to finish. If your smallest debt is also high-rate, the strategies converge. Honest rule: pick avalanche if you're a spreadsheet person, snowball if you've tried and quit before, and don't agonize — the extra payment matters ten times more than the ordering.
Making the snowball bigger
The payoff date is driven almost entirely by total monthly payment versus total balance. Before optimizing order: call card issuers for a rate reduction, consider a 0% balance transfer for the highest-APR card, sell something, and redirect any windfall (tax refund, bonus) to the target debt. Adding $100/month typically cuts more time off than switching strategies ever will.
How to use this calculator
List each debt with its current balance, interest rate, and minimum payment, then enter the total extra you can put toward debt each month beyond those minimums. The calculator runs both snowball and avalanche orderings and shows, for each, the payoff order, the date you'd be debt-free, and the total interest paid. Compare the two: if avalanche saves only a couple hundred dollars, the motivational edge of snowball's quick first win may be worth more than the math. Whichever you pick, the extra-payment figure is the real engine — increase it by even $50 and rerun to see how much faster the whole schedule collapses.