Snowball or Avalanche: The Gap Is Usually Smaller Than the Argument
One method is mathematically optimal. The other is the one more people finish. Here is how to tell which matters for you.
Both methods do the same thing
Pay the minimum on every debt. Take whatever is spare and throw all of it at one target. When that target clears, its minimum joins the pot and rolls into the next one — which is why both approaches accelerate, and why the last debt clears much faster than the first.
The only difference is which debt gets the spare money. Avalanche picks the highest interest rate. Snowball picks the smallest balance.
Avalanche always wins on arithmetic
Interest accrues on rate, not on size. Directing money at the highest rate always minimises total interest — this is not a matter of opinion, and avalanche can never cost more than snowball.
The honest question is how much more. Often the gap is a few percent of total interest and a month or two, because the highest-rate debt is frequently also small. Sometimes it is thousands. The calculator above tells you which case you are in rather than assuming.
When snowball is the better choice
Debt payoff fails from abandonment far more often than from choosing the wrong order. If clearing a small balance in two months is what keeps someone going, and the alternative is eleven months of grinding at a large balance with nothing visibly finished, snowball wins on the only metric that ends up mattering: completion.
The rule of thumb: if the calculator shows the gap is marginal, take the method you will stick to. If it shows a large gap, that is real money and worth some discipline.
The case where neither works
If a minimum payment is smaller than that debt's monthly interest, the balance grows no matter which method you pick, and it keeps growing until the extra payment finally reaches it. The calculator flags this explicitly because it changes the problem: the priority is finding more money or a lower rate, not optimising the order.
A balance transfer, consolidation loan or a negotiated rate reduction can beat both methods outright. Check the fee and the post-promotional rate before assuming it does.