Avalanche vs snowball: what the maths says

Both methods work the same way at the core: pay the minimum on every debt, then throw every spare pound or dollar at exactly one of them. They differ only in which one you target.

• Avalanche targets the highest interest rate.
• Snowball targets the smallest balance.

When a debt clears, its minimum payment rolls into the pot attacking the next one. That rolling effect is what makes both methods accelerate, and it is the part that matters most — far more than which order you choose.

Why avalanche is always cheaper

Interest accrues on balances at their own rate. A pound of principal removed from a 24% card prevents 24% of annual interest; the same pound removed from a 5% loan prevents 5%. Paying the highest rate first therefore minimises total interest, with no exceptions and no scenarios where the reverse holds. This is arithmetic, not an opinion.

Why the gap is often smaller than people expect

Here is the part that rarely gets said. The advantage of avalanche depends entirely on the shape of your particular debts, and in many real cases it is modest.

If your smallest debt also happens to carry your highest rate — a common situation, since small balances are often store cards and credit cards — the two methods target the same debt first and produce identical results. If your debts have similar rates, the gap is small. The difference only becomes large when you have a big balance at a high rate sitting alongside small balances at low rates.

This is why a general recommendation is less useful than running your own numbers. A few hundred saved is a different decision from several thousand saved.

The case for snowball

Clearing a whole debt is a discrete, visible event in a way that reducing a large balance by 8% is not. Removing an account entirely also simplifies life: one less minimum payment, one less statement, one less thing to forget.

If that momentum is what keeps you going for the eighteen months the plan takes, and the alternative is abandoning it in month four, snowball wins on the only metric that ultimately counts. The optimal strategy you quit halfway through loses to the second-best one you finish.

Three things that matter more than the order

1. Stop adding to the balance

No repayment strategy survives continued borrowing on the same cards. If the balance is still growing, the order of attack is not the problem to solve first.

2. Check whether a lower rate is available

A balance transfer or consolidation loan at a materially lower rate beats any reordering of payments at the old rate. Read two things before moving anything: the transfer fee, typically 3–5% of the balance, and the rate that applies after the promotional period ends. A 0% offer that reverts to 26% is a deadline, not a solution.

3. Take the employer match first

If your employer matches retirement contributions and you are not capturing the full match, that comes before extra debt payments — even before high-rate cards. An instant 50% return beats avoiding 24% interest. Capture the match, then attack the debt with everything else.

A note on minimum payments

Credit card minimums are usually calculated as a percentage of the outstanding balance, so they fall as the balance falls. This is why paying only the minimum stretches a card out for decades: the payment shrinks just as fast as the debt does. Most calculators, including ours, treat minimums as fixed, which means the true minimum-only payoff is slower and more expensive than the figure shown.