How the payoff actually works
Each month, interest is added to every balance first, then your payment is applied. Two things follow from that order: a month where your payment is smaller than the interest makes the balance grow, and every extra pound or dollar you send early removes interest that would otherwise compound for years.
All the minimums + your extra = your total monthly payment. This calculator holds that total constant. When a debt clears, its minimum does not disappear — it rolls onto the next target. That rollover is why the last debts fall so much faster than the first, and it is the whole mechanism behind both strategies.
Avalanche or snowball?
Avalanche attacks the highest APR first. It is arithmetically optimal — it always costs the least interest and is never slower.
Snowball attacks the smallest balance first. It costs more, sometimes trivially, sometimes a lot — but it removes a whole debt from your life sooner, and for many people that first win is what keeps the plan alive.
The honest answer is to run both above and look at the gap. If avalanche saves the price of a coffee a month, take snowball and enjoy the momentum. If it saves thousands, that is the real cost of the motivation, and worth knowing before you choose.
Where these numbers can mislead
- Real minimums usually shrink. Card issuers recompute the minimum as a percentage of the balance, so it falls as you pay down. Holding it constant — as this calculator does — is both the more aggressive plan and the one that actually clears the debt. Expect your statement's minimum to drift below the figure you entered.
- APR is not the whole cost. Annual fees, late fees and promotional rates that expire partway through are not modelled here.
- New spending breaks the projection. The forecast assumes nothing further is added to these balances.
- Check for a 0% transfer first. Moving a high-APR balance into a 0% window can beat any ordering strategy outright — just count the transfer fee and what the rate reverts to.
The number that matters most
It is not which strategy you pick. It is the extra payment. Raising the extra improves both strategies far more than choosing between them ever will — change it above and watch the debt-free date move. If the extra is zero and the date still looks distant, the useful next question is about income or interest rate, not ordering.