Debt Snowball Calculator

Mathematically, the avalanche method (paying highest-interest debt first) always pays off debt faster and cheaper than snowball (paying smallest balance first). On a typical UK debt mix - £5,000 credit card at 18.9%, £15,000 car loan at 4.5%, £25,000 student loan at 3.1% - with £200 a month extra, avalanche saves around £1,200 in interest and clears the debt roughly two months sooner than snowball. The gap widens with higher-rate debts.

Snowball wins on behaviour, not maths. Clearing a £500 store card in three months gives you a visible win, freeing up that minimum payment as ammunition for the next debt and building momentum. Studies of actual debt-payoff completion rates (most notably by Ramsey Solutions and academic work by Gal and McShane) suggest people stick with snowball at higher rates because the early wins are motivating. If you have tried and abandoned the avalanche before, snowball may be the right call even though the calculator shows it costs more.

If your highest-rate debt is dramatically more expensive than the rest (a 39% APR store card alongside two sub-5% loans), avalanche is almost always the right call regardless of personality, because the interest gap is too large to ignore. £3,000 on a 39% store card accrues £100 a month in interest alone. Throwing snowball payments at the £500 sub-5% personal loan first because it is smaller is a behavioural luxury that costs roughly £500 over the payoff timeline.

If your debts are all in a narrow rate band (say 6% to 9%), the maths of avalanche barely beats snowball, and the behavioural pull of snowball usually wins. The calculator shows you the exact pound difference between the two methods so you can make the call with eyes open. Below £500 difference over the whole payoff, most people who choose snowball stick with it; above £2,000 difference, most people switch to avalanche once they see the number. The [debt payoff calculator](/debt-payoff-calculator) lets you test the same debts under both strategies side by side.

The calculator assumes you keep adding the same monthly extra payment until the last debt is gone, and that you do not run any of the cleared cards back up. In practice, the second assumption is the one that breaks. Lender data published by UK Finance shows roughly one in three borrowers who consolidate or clear credit card debt return to a meaningful balance within 18 months. The behavioural fix is to either close the cleared card, lock it in a drawer, or set it to direct-debit-pay-in-full each month so that any new spend triggers an immediate full repayment. None of those fixes show up in the calculator output, but they are the single biggest determinant of whether the projected debt-free date actually arrives.