Debt Snowball Calculator
Model the snowball payoff method — pay minimums on every debt, then send every spare pound or dollar at the smallest balance until it clears, then roll its payment into the next-smallest balance.
Months to debt-free
25 months (2.1 years)
- Total paid
- £12,358.95
- Total interest paid
- £2,358.95
- Starting balance
- £10,000.00
- Payoff order (smallest balance first)
- Debt 3 → Debt 2 → Debt 1
Pay every debt its minimum each month, then send everything left from your monthly budget to the smallest balance. As each debt clears, its payment rolls into the next-smallest balance — that is the "snowball" effect.
How to use this calculator
Enter the balance, APR, and minimum monthly payment for up to three debts — credit cards, personal loans, store cards, anything compounding monthly. Then enter the total monthly amount you can put toward debt (this must cover the sum of the minimums, with something left over to actually make progress). The calculator locks in the snowball order at the start by sorting your debts smallest balance first, then simulates month-by-month payments, applying interest, paying every minimum, then throwing every remaining penny at the smallest balance. As each debt clears, its payment rolls into the next one in the snowball order. You get the total months to debt-free, the total amount you will pay, the total interest, and the order in which your debts get cleared.
How the calculation works
The snowball method ignores APR and focuses entirely on momentum. You list your debts by balance, smallest first, then attack the smallest one until it clears — regardless of whether it is the most expensive. The idea is psychological: clearing whole debts quickly produces visible wins that help most people stick with the plan, even though chasing the smallest balance is mathematically suboptimal. Each month the simulator applies interest at r = APR/12 to every surviving balance, pays each debt its minimum (capped at the remaining balance), then sends the leftover budget to the smallest starting balance until it clears, then to the next-smallest, and so on. When a debt hits zero its minimum payment joins the surplus pool — this rolling payment effect is the "snowball" growing as you go, and it is why later debts clear much faster than the first one. The simulation stops when every balance is cleared, or after 50 years if the budget is too small to keep up with interest.
Worked example
Three debts: 5,000 at 22% APR (100/mo min), 3,000 at 18% (75/mo min), and 2,000 at 15% (50/mo min). Total minimums: 225/mo. With a 500/mo budget, the snowball order is locked by starting balance: Debt 3 (2,000) → Debt 2 (3,000) → Debt 1 (5,000). The first month accrues about 91.67 + 45.00 + 25.00 = 161.67 in interest. After minimums, 275 of surplus goes to Debt 3 — the smallest balance — even though Debt 1 has the highest APR. Debt 3 clears in roughly 7 months, freeing its 50 minimum. Debt 2 clears next, freeing 75 more. Debt 1 then gets the full 500. Total payoff is roughly 26 months with about 2,200 in interest — a few months longer and a couple of hundred pounds or dollars more expensive than the avalanche method on the same debts, but the trade-off is the fast early win on Debt 3.
Frequently asked questions
What is the difference between the debt snowball and debt avalanche methods?
Both pay minimums on every debt and direct any extra money at one chosen debt until it clears. The snowball attacks the smallest balance first, regardless of APR — the idea is to rack up quick wins by clearing whole debts, which keeps motivation high. The avalanche attacks the highest-APR balance first because that is the one compounding fastest, which minimises total interest paid. The avalanche is mathematically optimal. The snowball is psychologically optimal. For the same set of debts, the snowball typically costs a bit more and takes a bit longer than the avalanche, but the gap is often smaller than people expect — and if the snowball is what gets you to stick with a plan you would otherwise abandon, the extra interest is well spent.
Why does the snowball method ignore APR?
On purpose. The whole premise is behavioural: a US National Bureau of Economic Research study (Gal & McShane, 2012) and a 2016 Harvard Business Review write-up of a Kellogg School study found that people who focused on closing small accounts first were more likely to stick with their debt-payoff plan than those targeting the highest-rate account, even though the latter is cheaper on paper. If you have tried and failed to stick to a debt plan in the past, the snowball is a reasonable choice — you pay a little more interest in exchange for momentum. If you are confident you will follow through regardless, the avalanche saves you money.
Does my budget have to cover all the minimum payments?
Yes — and it has to cover the sum of the monthly interest charges across every debt, or the total balance will grow rather than shrink. If your budget is less than the combined first-month interest, the calculator returns "never clears". This is the multi-debt version of the credit card minimum-payment trap. If you cannot cover the minimums, neither method applies — at that point you are in a hardship situation and should consider a balance transfer, hardship plan with the issuer, or non-profit credit counselling (the CFPB in the US and StepChange or Citizens Advice in the UK both offer free guidance).
What happens when a debt is paid off — does the snowball get bigger?
Yes, and that is exactly where the name comes from. When Debt 3 (the smallest) clears, the money that was going to its minimum payment (plus all the surplus that was attacking it) is freed up and rolls automatically onto Debt 2. So your effective monthly attack on Debt 2 is now much larger than what you started with — and your monthly attack on Debt 1 is larger still when Debt 2 clears. Each cleared debt accelerates the next one, which is why total payoff time is a small fraction of what each debt would take in isolation. The "snowball" rolling downhill, getting bigger as it goes.
Should I include my mortgage in this calculator?
Usually no. Both the snowball and avalanche methods are designed for unsecured, high-interest, revolving or short-term debt — credit cards, store cards, personal loans, payday loans, BNPL balances. Mortgages and student loans typically have much lower APRs and longer terms, and there are often tax or refinancing considerations that change the maths. Use this for your high-APR debts first; clear them; then separately decide whether early mortgage repayments make sense for your situation.
Why does the calculator only support three debts?
Three is the right balance between usefulness and form length — most people with high-interest debt have one to three problem balances driving the cost, and modelling those captures the snowball dynamic completely. If you have four or more, group the lowest-priority balances (largest by balance) into a single row by summing their balances, taking the weighted average APR, and summing their minimums. The total payoff time and interest will be a very close approximation to a full per-debt simulation, and the attack order is still correct: smallest balance first.