About the Debt Snowball Calculator
Two ways to order paying off several debts, and a long-running argument about which is right.
Avalanche attacks the highest interest rate first. It is mathematically optimal — no other ordering clears the debts for less money.
Snowball attacks the smallest balance first. It costs more, and it closes accounts sooner, which people find motivating.
The argument is usually conducted without numbers. This debt snowball calculator computes both and reports exactly what choosing snowball costs, because that is the only thing that makes the trade-off decidable.
How to Use the Debt Snowball Calculator
Enter what you can put towards these debts each month in total, including the minimums — not on top of them.
Then up to four debts, each with a balance, a rate and a minimum payment. Leave unused slots at zero.
Step-by-Step Example
£900 a month against three debts:
| Debt | Balance | Rate | Minimum |
|---|---|---|---|
| 1 | 1,200 | 19.9% | 35 |
| 2 | 8,000 | 24.9% | 200 |
| 3 | 4,500 | 6.5% | 150 |
Avalanche (highest rate first): 18 months, 1,762.93 interest
Snowball (smallest first): 18 months, 2,399.61 interest
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Snowball costs: 636.67Both finish in the same month. The difference is £636.67 of interest — 4.65% of what is owed.
In exchange, snowball clears its first debt at month 3 instead of month 13.
How Both Methods Actually Work
The part that matters is the same under either ordering, and it is not the ordering.
Every debt gets its minimum. Missing one triggers fees, penalty rates and credit damage that dwarf any interest saved.
All spare money attacks one target. In the example, £900 minus £385 of minimums leaves £515 going at a single debt.
When a debt clears, its whole payment rolls into the next. Clear debt 1 and its £35 minimum plus the £515 now attack debt 2.
That rolling is what makes either method accelerate — each cleared debt makes the next one faster. The orderings only decide which debt is first in line.
What the Cost Depends On
The gap between the two methods is not fixed. It depends on how your debts happen to line up.
Cheapest when they agree. If your smallest balance also carries the highest rate, both methods start in the same place and snowball is free.
Widest when the smallest is also the cheapest. Then snowball spends months attacking the one debt costing you least while your most expensive balance keeps accruing. That is where the cost climbs.
The calculator works out which case you are in rather than asserting one, because the usual explanation — "the smallest debt is the cheapest" — is often not why the gap exists on real inputs.
So Which Should You Choose?
A rule that actually decides it:
Below about 2% of what you owe, take the snowball. A plan you finish beats a cheaper plan you abandon, and the evidence on completion rates is not close. The early win is worth more than the money at that scale.
Above about 2%, it deserves a deliberate decision rather than a default. You are buying motivation with real money, and it is worth knowing the price. If you have finished a debt plan before and know you will finish this one, take the avalanche.
In the example above, £636.67 for clearing a debt ten months earlier is a genuine judgement call. Some people would pay it happily. The point is to make that choice knowingly.
When Neither Method Works
If your budget barely exceeds the minimums, almost nothing is attacking any balance and neither ordering clears in a sensible time.
The lever there is not the ordering. It is the budget or the interest rates — a balance transfer or a consolidation loan changes the picture far more than any sequencing can.
The calculator says so rather than producing a figure, and a free debt advice service is the right next step. They are free, they are used to this, and they have options a calculator does not.
Understanding Your Result
What snowball costs leads with the difference in money, because the two methods often finish in the same month while the interest differs by hundreds.
Highest rate first and smallest balance first give each method in full.
The trade-off puts the cost as a share of what you owe, against how much earlier the first debt clears.
Worth knowing gives the verdict, and explains where the gap came from.
When Should You Use This Calculator?
Before starting a debt plan. Choosing an ordering knowingly is the point.
When you have three or more debts. With one or two the orderings usually agree.
After clearing a debt. The picture changes, and so might the best order.
When someone tells you one method is obviously right. Both camps are confident; only the numbers are specific.
Common Mistakes
Arguing about the methods without computing the gap. It is often small enough that the argument does not matter.
Assuming avalanche is always meaningfully better. It is always at least as good, and sometimes by an amount not worth the abandoned plan.
Redirecting money away from minimums. Never. Fees and penalty rates cost more than the interest saved.
Forgetting the rolling. Both methods work because cleared payments roll onward. Spending that freed money instead is what actually breaks a plan.
Ignoring a balance transfer. Moving the expensive debt to 0% does more than any ordering — the credit card payoff calculator covers that.
Taking on new debt while paying these off. It resets the whole plan and is the most common reason people repeat it.
Every figure here is an estimate for planning. This is not financial advice, and if the debt is unmanageable a free debt advice service is the right place to go.