How the debt avalanche works
Pay the minimum on everything, then send every spare dollar to the highest-rate debt regardless of its size. When it clears, that entire payment rolls into the next highest rate. Because the most expensive balance shrinks fastest, less interest accrues overall than in any other payoff order.
This is provably the cheapest order. No arrangement of the same payments against the same debts produces less interest than paying highest rate first.
When the avalanche is clearly worth it
The gap over the snowball widens when your highest-rate debt also carries a large balance — a maxed card at 27% behind several small low-rate loans, for example. In that setup the snowball can leave the expensive balance untouched for a year while interest piles up.
When your rates are close together, the two methods land within a few dollars of each other. In that case pick whichever you will stick with, and check the numbers on the debt snowball calculator.
Rate details that change the order
Cash advance and balance transfer portions of a card often carry a different, higher APR than purchases — enter them as separate lines if they are significant. Variable rates move with prime, so re-check your order once or twice a year.
Also weigh secured debt separately. A car loan at a lower rate can still deserve priority if you are at risk of repossession, and tax debt carries penalties that a stated rate understates.
Common mistakes
Sorting by balance instead of rate, forgetting a promotional rate that expires and jumps, and abandoning the plan because progress feels slow on a large first target. If motivation is the real problem, the snowball's faster first win is a legitimate reason to switch.