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The math says avalanche. The finish line says pick what you will actually do.
Both strategies pay every minimum every month — they differ only in where the extra money goes. Avalanche attacks the highest APR and is always the mathematical optimum; snowball attacks the smallest balance for faster psychological wins. This calculator runs a real month-by-month simulation of both on your actual debts — interest accrual, freed-up minimums rolling into the attack payment, payoff order — so the dollar difference is exact, not a rule of thumb.
Anyone carrying two or more debts uses it to end the strategy debate with their own numbers: the exact dollar and month difference between attacking the highest rate and attacking the smallest balance. It turns the loudest argument in personal finance into a five-minute decision.
Avalanche always wins mathematically — highest APR first minimizes total interest. Example: a $1,500 card at 12% and a $4,000 loan at 20%, with $100 extra monthly, avalanche saves $296 in interest and finishes 2 months sooner ($1,222 vs $1,519 interest, 31 vs 33 months). Snowball wins behaviorally for many people: the quick first payoff keeps them going. The best plan is the one you finish.
Usually less than people expect — both strategies concentrate the same total payment on one debt at a time, so the gap is only the interest on the ordering difference. When your highest-APR debt is also your smallest, the two strategies are identical. The gap grows with big rate spreads and big balance differences in the wrong direction.
Generally no. Mortgages carry the lowest rate in most portfolios and offer tax advantages and long fixed terms; avalanche logic applied across a whole life usually ranks them last anyway. Run this calculator on consumer debts — cards, personal loans, auto loans — and treat the mortgage separately.