Both methods start the same way
Pay the minimum on every debt, then put everything extra you can afford towards one target debt. When it is paid off, add its payment to the next target, so the amount you throw at debt grows as each one disappears. The two methods differ only in the order.
Avalanche: highest interest rate first
Target the debt with the highest interest rate. This always costs the least interest overall and usually makes you debt free soonest. It is the choice on the numbers alone.
Snowball: smallest balance first
Target the smallest balance, whatever its rate. You clear the first debt quickly, which gives a sense of progress and fewer bills to track. The cost is some extra interest, which is small when the rates are similar and larger when a big balance carries a high rate.
Which to choose
The method you stick with beats the one you give up on. If you need early wins to keep going, snowball. If you are motivated by the total saved, avalanche. Either one is far better than paying only the minimums, which can take decades on a credit card.
Compare them with your debts
Enter your balances, rates and minimums in the Debt Snowball vs Avalanche Calculator to see the months to debt free, the total interest and the payoff order for both. For a single card, the Credit Card Payoff Calculator shows how long a fixed payment takes.