The same debts run under both strategies — what each one costs you, and how much sooner you finish.
Two ways to order the same repayments. Avalanche attacks the highest interest rate first and always costs less. Snowball attacks the smallest balance first and clears debts sooner, which is easier to keep going. This runs your actual numbers through both, month by month, so you can see what the behavioural choice is really costing.
#DebtBalanceAPR %Min/mo
The extra is what you can pay above the combined minimums. It all goes to one debt at a time — that is the entire difference between the two strategies.
£0.00
Avalanche saves you
Combined minimum payments—
Total you are putting in—
Side by side
Snowball
Avalanche
Snowball payoff order — smallest balance first
Order
Debt
APR
Cleared
Interest on it
Avalanche payoff order — highest APR first
Order
Debt
APR
Cleared
Interest on it
Each debt, both ways
Debt
Balance
APR
Snowball
Avalanche
Assumes fixed APRs for the whole run, no new borrowing, no fees or charges, payments applied at the end of each month, and interest compounded monthly at the APR divided by twelve. When a debt clears, its minimum payment rolls onto the next target in the same month. Ties are broken by the order the rows are in. The simulation stops at 50 years.
About this calculator
The mathematical case for avalanche is not really an argument, it is a definition. Interest accrues in proportion to the rate, so every pound of the extra payment removes the most future interest when it is aimed at the highest rate. Any other order leaves cheaper debt cleared early while dearer debt keeps compounding. Avalanche is therefore always equal to or cheaper than snowball, never worse — and it is equal only when the two happen to put the debts in the same sequence anyway.
The behavioural case for snowball is that people are not spreadsheets. Clearing a debt entirely is a visible, finished thing in a way that shaving interest off a large balance is not, and the account that disappears in month four is what keeps someone paying in month twenty. Research on this — the best known being work out of Northwestern's Kellogg School — has found that people who tackle the smallest balance first are more likely to stay with the plan and clear their debts, even though it costs more on paper. A slightly more expensive plan you finish beats a cheaper one you abandon in month six.
The gap between the two is usually much smaller than people expect — often tens of pounds across a whole repayment plan, not hundreds. This is because the extra payment does most of the work whichever debt it lands on, and because both strategies clear everything in a broadly similar time. Run your own figures above rather than assuming: if the difference comes out at the price of a takeaway, the choice is purely about which one you will actually keep to.
There is one case where the gap is genuinely large, and it is worth knowing whether you are in it. If a small balance carries a very high rate — a store card at 30% with £400 on it, sitting alongside a £9,000 car loan at 6% — then the two strategies happen to agree, because the smallest balance is also the dearest. The expensive case is the reverse: a large balance at a very high rate next to a small cheap one. Snowball then spends months clearing something trivial while the expensive debt compounds, and the difference can run into hundreds. The larger the spread between your highest and lowest APR, and the bigger the balance sitting at the top rate, the more avalanche is worth.
Two things that matter more than either strategy. Clearing high-interest debt beats investing: paying off a card at 22% is a guaranteed 22% return, which no investment reliably offers, so debt at anything above about 8–10% should almost always come first. And a 0% balance transfer changes the picture entirely — move a balance to 0% for eighteen months and its APR becomes irrelevant for that period, which reorders the whole plan. If you can get one, do that first and then run these numbers again on what is left. Watch the transfer fee, typically 2–4%, and what the rate reverts to.
This page is about choosing the order to clear several debts. For the month-by-month schedule of a single loan — the payment, the interest split, the balance each year — use the loan repayment calculator instead.
Frequently asked questions
What is the difference between the debt snowball and the debt avalanche?
Both pay the minimum on everything and put every spare pound at one debt. They differ only in which one. Snowball picks the smallest balance, so debts disappear quickly and you get visible wins early. Avalanche picks the highest APR, so you remove the most expensive interest first. Avalanche always costs the same or less; snowball is easier to stay with. The order is the entire difference — everything else about the plan is identical.
Is the avalanche method always cheaper?
Cheaper or equal, never more expensive. That falls out of the arithmetic: interest accrues in proportion to the rate, so a pound aimed at your highest rate always removes at least as much future interest as the same pound aimed anywhere else. The two come out identical when your debts happen to rank the same way by balance as by rate, which is more common than you would think. What varies is the size of the gap, not its direction.
If avalanche is cheaper, why would anyone use snowball?
Because finishing the plan matters more than optimising it. Clearing an account outright is a concrete result that keeps people going, and studies of real repayment behaviour find that people who start with the smallest balance are more likely to stick with the plan and clear their debts. If the difference on your own figures is small — and it usually is — the strategy you will actually keep to is the better one.
Should I pay off debt or invest?
Clearing debt at 22% is a guaranteed 22% return, and no investment offers that reliably. As a rule of thumb, anything above roughly 8 to 10% should be cleared before investing beyond an employer pension match, which is free money and comes first. Below that the case gets closer, and a student loan on income-contingent repayment is a different question entirely. Keep a small emergency fund regardless, or the next unexpected bill goes back on the card.
What if my minimum payment does not cover the interest?
Then that balance grows every month and never clears on its own. The calculator flags this against the specific debt, because it changes the plan: that debt has to be the target regardless of which strategy you prefer, or nothing else you do will work. If the numbers do not add up at all, a 0% balance transfer or free debt advice from StepChange or Citizens Advice is the right next step rather than a repayment ordering.
Does a 0% balance transfer change which strategy to use?
Substantially. A balance at 0% accrues nothing, so avalanche correctly ranks it last and you pay only the minimum on it while attacking everything else. The thing to watch is the end of the promotional period — set a reminder, because the reverted rate is often higher than what you left. Factor in the transfer fee too, usually 2 to 4% of the balance, which is a real cost paid up front.