Debt Snowball vs Avalanche: What the Choice Actually Costs

Corrected 4 August 2026. An earlier version of this calculator could report the avalanche method losing money against the snowball. That is impossible: paying the highest rate first cannot cost more interest. The fault was in how the formula handled a debt that finishes earlier than expected, and it has been rebuilt and checked against a month-by-month simulation across roughly 25,000 scenarios. Every figure on this page is from the corrected version. If you used this page before that date, the interest comparison it showed you may have been wrong.

The argument, priced

Two debts — $3,000 at 6% and $12,000 at 22% — with $200/month spare above the minimums.

• Avalanche (highest rate first) saves $866 in interest
• Snowball (smallest balance first) clears your first debt in 11.2 months instead of 31.9

That's 20.7 extra months of paying diligently without ever crossing anything off a list, in exchange for $866.

Neither of those is the wrong answer. But now it's a decision instead of an argument.

The two methods differ in exactly one way

Both pay every minimum, every month. Both roll a cleared debt's payment into the next one — that rolling is where the momentum comes from in either case, and it's why people conflate them.

The single difference is where your spare money goes:

• Snowball → smallest balance
• Avalanche → highest interest rate

Everything else about the two plans is identical.

Avalanche never costs you more

Putting your spare money against the highest rate is never the more expensive choice. When the two methods target different debts, avalanche saves strictly more. When they target the same debt — which happens whenever your smallest balance is also your highest rate — the two plans are identical and the saving is exactly $0.

There is no combination of balances, rates and minimums where snowball comes out ahead on interest.

The genuinely open question is how much less — and here, on a $15,000 principal, it's $866. That's about 5.8% of what you owe, and 17% of the total interest.

Worth having. Also worth knowing the exact size of before deciding it settles the argument.

Snowball never waits longer for the first win

Which is the thing its advocates are actually arguing about, and the money comparison hides it completely. Snowball either gets you there sooner or ties — it is never the slower of the two.

Note that the first debt to disappear isn't always the one you're aiming at. Under avalanche, a small cheap debt sitting on its minimum can finish before the expensive one you're attacking, and the tool counts that as your first win, because it is one.

On these numbers avalanche makes you wait nearly three years before a single debt disappears. Snowball gets you there in under a year.

If you've started a debt plan before and stopped, that gap isn't a soft consideration — it's the thing that decides whether the plan survives at all.

Sometimes there's no decision to make

The two strategies only diverge when your small debt is the cheap one.

If your smallest balance also carries your highest rate — which is extremely common, because small credit card balances often carry the worst rates — both methods pick the same debt, and the calculator will show a saving of exactly $0.

That's a real answer, not an error. It means the thing you've been agonising over doesn't matter. Start.

How the maths works

A closed form in two phases — with one branch that matters more than it looks.

Phase 1: the target debt gets its minimum plus your extra; the other accrues interest and pays only its minimum. Each debt has a month count at which it would clear on whatever it's being paid:

n = −log(1 − i × balance ÷ payment) ÷ log(1 + i) months

The branch: phase 1 ends when the first debt clears — and that is not always the one you're targeting. Avalanche in particular leaves a small, cheap debt sitting on its minimum while you attack the expensive one, and that small debt often finishes first. Whichever goes first, the other's balance at that moment is exact:

B(1 + i)ⁿ − m((1 + i)ⁿ − 1) ÷ i

Phase 2: the whole monthly outlay — both minimums and the extra — goes at whatever's left.

Your monthly outlay never changes across either phase; only the split between the two debts does. So the total paid is that outlay multiplied by the total months, and the total interest is that minus what you originally owed.

Two debts, not ten — and that's deliberate

A tool here is a specification, not a program. It holds formulas, not a loop, so it can't walk an arbitrary list of debts.

Two is the smallest case that demonstrates the entire effect — and small enough to solve with a formula rather than a simulation.

The principle doesn't change with ten debts: the ordering rule is identical, and the gap between the strategies generally widens. If you have ten, the honest use of this page is to model your smallest balance against your most expensive one and see how far apart they are. That's the decision in miniature.

Three honest caveats

The months are fractional — round them up. The closed form lets the final payment be a part-month, so the figure shown sits just below the month you actually finish in. Rounded up, it is the real month: across 6,860 test scenarios that was exact in 99.9% of them, and out by a single month in four. The interest figures are the comparison the tool leads with, and they land within a few dollars of a full month-by-month schedule.

Some combinations have no answer, and the tool says so. If neither debt can clear on what it's being paid — because the minimum doesn't even cover that month's interest — there's no payoff schedule to compute, and the figures read "—" rather than guess at one.

Minimum payments are assumed fixed. A real credit card recalculates the minimum as a percentage of the balance, so it falls as you pay down — which stretches the payoff and costs more interest than modelled. Enter what you're actually paying now and treat the result as the optimistic case. It doesn't change which strategy wins; it makes both slower than shown.

What to actually do

Pick the one you'll finish.

An avalanche abandoned in month eight costs far more than a snowball completed. That isn't a motivational sentiment — it's the dominant term, and it's the one thing on this page no formula can model for you.

So use the tool to find out what the choice really costs:

• Saving small, first-win gap long? Take the snowball, without guilt
• Saving large, and you're confident you'll see it through? Take the avalanche
• Comes out at $0? Stop reading and start paying