Debt Snowball vs Avalanche: What the Numbers Actually Show
We ran both methods month by month on realistic UK debts rather than repeating the usual claims. The results are less dramatic than you have been told.
Almost every article on this subject says the same thing: the avalanche saves you “hundreds or even thousands of pounds”, but the snowball keeps you motivated. The second half is fair. The first half is usually wrong, and it is wrong in a way that matters.
We simulated both methods month by month, compounding interest at each debt's real rate, on two realistic UK debt profiles. On the typical one, the avalanche saved £30 across 31 months and both methods cleared the debt in the same month. Here is the working.
The two methods, briefly
Both work the same way mechanically. You pay the minimum on every debt, then throw every spare pound at one priority debt. When that debt clears, its whole payment rolls onto the next. The only difference is how you choose the priority.
- Snowball: smallest balance first, regardless of rate. Wins come quickly, which keeps people going.
- Avalanche: highest interest rate first, regardless of balance. Mathematically optimal on total interest.
Simulation 1: a typical UK debt mix
Four debts totalling £15,000, minimum payments of £350 a month, and £250 a month of spare capacity on top — a £600 monthly budget.
| Debt | Balance | Rate | Minimum |
|---|---|---|---|
| Store card | £1,200 | 34.9% APR | £30 |
| Overdraft | £1,500 | 39.9% EAR | £40 |
| Credit card | £4,800 | 24.9% APR | £120 |
| Personal loan | £7,500 | 9.9% APR | £160 |
The snowball attacks the store card first (smallest balance), then the overdraft. The avalanche attacks the overdraft first (highest rate), then the store card. After the first two debts the orderings are identical. That single fact explains the whole result.
| Snowball | Avalanche | |
|---|---|---|
| Debt-free in | 31 months | 31 months |
| Total interest paid | £3,084 | £3,054 |
| First debt cleared | Month 5 (store card) | Month 6 (overdraft) |
| Second cleared | Month 10 (overdraft) | Month 10 (store card) |
| Third cleared | Month 22 (credit card) | Month 22 (credit card) |
| Fourth cleared | Month 31 (loan) | Month 31 (loan) |
Interest compounded monthly at (1 + APR)1/12 − 1. Minimum payments held constant. Simulated to the month, not estimated.
The avalanche advantage is £30. That is 1% of the total interest, and about a pound a month. It is not nothing, but it is not a reason to override a plan you find easier to stick to.
And this is not a rigged example. It is the shape most UK debt actually takes: the small debts are the expensive ones. Store cards, overdrafts and catalogue accounts carry the highest rates and the lowest balances; personal loans and car finance are large and comparatively cheap. When balance order and rate order broadly agree, snowball and avalanche converge.
Simulation 2: when the avalanche genuinely wins
Now flip it. Here the largest balance is also the most expensive — someone who has run up a big credit card alongside a small, cheap car finance agreement.
| Debt | Balance | Rate | Minimum |
|---|---|---|---|
| Car finance | £800 | 5.9% APR | £25 |
| Loan | £2,000 | 12.9% APR | £60 |
| Credit card | £9,000 | 29.9% APR | £225 |
| Snowball | Avalanche | |
|---|---|---|
| Debt-free in | 29 months | 27 months |
| Total interest paid | £3,939 | £3,233 |
| Difference | Avalanche saves £705 and two months | |
Here the avalanche is worth 17.9% of the interest bill, and the snowball's cost is real. The snowball spends its first nine months clearing a £2,800 of cheap debt while a £9,000 balance compounds at 29.9%.
So the rule is not “avalanche is better”. It is much more specific:
The avalanche is worth choosing when your largest balance also carries your highest rate. When your smallest debts are your most expensive, the two methods are nearly the same plan and you should pick whichever you will actually finish.
You can check this in ten seconds. List your debts by balance, then list them by rate. If the two lists look similar, the choice barely matters. If they are close to reversed, take the avalanche seriously.
The counter-intuitive bit: paying more shrinks the gap
You would expect that putting more money in makes the better method pay off more. The opposite is true. Same four debts from simulation 1, varying only the spare monthly capacity:
| Extra per month | Snowball | Avalanche | Avalanche saves |
|---|---|---|---|
| £50 | 55 months, £6,765 | 55 months, £6,611 | £154 |
| £100 | 45 months, £5,068 | 45 months, £4,988 | £81 |
| £250 | 31 months, £3,084 | 31 months, £3,054 | £30 |
| £500 | 20 months, £1,942 | 20 months, £1,929 | £14 |
| £800 | 15 months, £1,375 | 15 months, £1,367 | £8 |
The ordering only matters while the debt is outstanding, so the faster you clear it, the less room there is for the ordering to do any damage. The method matters most to the people with the least spare money, which is the reverse of how it is usually presented.
Look at the same table a different way, though. Going from £50 to £250 a month cut the interest bill by £3,681 and the timeline by two years. Every choice on this page is worth less than finding another £50 a month. If you only take one thing away, take that one.
What the behavioural evidence says
The case for the snowball has never really been mathematical. It is that people finish. Clearing an entire account is a discrete, visible win in a process that otherwise offers very little feedback for months at a time, and the research on debt repayment consistently finds that closing accounts early is associated with sticking with the plan.
Set that against a typical cost of £30 and the argument is not close. The failure mode that should worry you is abandoning the plan in month four, not choosing the second-best ordering.
The hybrid, and when it costs you nothing
A common suggestion is to clear one small debt for the win, then switch to avalanche order. On simulation 1 this costs essentially nothing, because the smallest debt was second in the avalanche order anyway. On simulation 2 it costs more, because the small cheap car finance is genuinely the wrong place to start.
Which is the same test again: check whether your balance order and your rate order agree before deciding how much the hybrid costs you.
Before you optimise the order, check these
- A 0% balance transfer beats both methods outright. Moving the £4,800 credit card in simulation 1 to a 0% deal saves far more than the £30 the ordering is worth, even after a 3% transfer fee.
- Ask for a lower rate. Reducing an overdraft or card rate changes the arithmetic permanently and costs a phone call.
- Check the minimum payment trap. Paying only the minimum on a credit card can take decades — see our guide on the minimum payment trap.
- Keep a small buffer. Throwing every last pound at debt and then borrowing again when the boiler breaks undoes months of progress.
Frequently asked questions
Does the debt avalanche really save thousands of pounds?
Rarely. On a typical UK debt mix, where the small debts (store cards, overdrafts) are also the expensive ones, the two methods produce almost the same repayment order. In our simulation of 15,000 pounds across four debts, the avalanche saved 30 pounds over 31 months and both methods finished in the same month. The large savings you see quoted come from cases where the biggest balance is also the highest rate.
When is the avalanche clearly worth it?
When your largest balance carries your highest interest rate. In our second simulation, a 9,000 pound credit card at 29.9% alongside a small cheap car finance balance, the avalanche saved 705 pounds and finished two months sooner. That is a real difference worth overriding your instincts for.
Does the gap get bigger if I pay more each month?
No, it gets smaller. On the same debts, an extra 50 pounds a month made the avalanche worth 154 pounds, while an extra 800 pounds a month made it worth 8 pounds. The faster you clear the debt, the less time there is for the ordering to matter. So the method matters most to people with the least spare cash.
Should I use the snowball if I struggle to stay motivated?
Probably, and the cost of doing so is usually small. Given that the typical gap is tens of pounds rather than thousands, the risk of abandoning a plan is a far bigger financial threat than picking the theoretically worse ordering. A plan you finish beats a plan you optimise.
Is there a way to get both?
Yes. Clear one small debt first for the psychological win, then switch to avalanche order for the rest. On our typical mix this hybrid costs almost nothing, because the first small debt was near the top of the avalanche order anyway.
Run it on your own debts
The tables above are one debt profile each. Yours will differ, and the only number that matters is yours. Put your actual balances, rates and minimums into the debt payoff calculator to see both methods side by side with your real payoff dates and interest totals.
See also: how to pay off debt fast and getting out of debt in the UK.
Method, assumptions and help
Both simulations were run month by month in code rather than estimated. Interest is applied monthly at (1 + APR)1/12− 1, then payments are applied: minimums to every live debt, then all remaining capacity to the priority debt, with cleared debts' payments rolling forward. Minimum payments are held constant rather than reducing with the balance, which is a simplification — in practice percentage-based card minimums fall over time, which slightly lengthens both methods without materially changing the gap between them. Rates and balances are illustrative and chosen to be representative of UK products; they are not published averages.
SnowballCalc is published by CJ Software Ltd. This page is general information, not debt advice. If you are struggling with debt, free and impartial help is available from StepChange, National Debtline and Citizens Advice. Last reviewed August 2026.