Each month
Interest is added: balance × (APR/100) / 12. Then every debt receives its minimum (or the remaining balance if smaller). Leftover budget goes to the target: highest APR (avalanche) or smallest balance (snowball).
Budget
Budget = sum of minimums + extra. It does not automatically rise when a card is paid off except that the freed minimum stays in the pool — the extra is applied after remaining minimums.
Minimums-only baseline
The same engine with extra = 0. Interest saved is that total minus the better of avalanche/snowball.
FAQ
Daily compounding?
Not modelled. Monthly is the usual card statement convention used here.
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