Highest rate first — pay the least interest possible.
The avalanche attacks your highest APR first, no matter the balance. You pay minimums on everything, then throw every extra dollar at the most expensive debt until it is gone — then roll that payment into the next highest rate. Every dollar fights the maximum interest.
Run the same debts through both this and the snowball calculator and compare the total interest. When the rates are far apart, the avalanche can save you hundreds or thousands. When they are close, pick whichever plan you will actually stick with.
Avalanche, always — attacking the highest rate first minimizes total interest by definition. The snowball only wins on motivation, never on math.
Yes. You always pay every minimum (to avoid fees and damage), and the extra goes to the highest-rate balance. The calculator handles the minimums for you.
Treat it carefully: a 0% rate sorts last in the avalanche, but if the promo expires soon and the deferred interest is brutal, prioritize beating that deadline. Math serves the plan, not the other way around.
When rate gaps are big — say a 24% card versus a 7% personal loan. The bigger the spread, the more the avalanche saves you.