Debt Payoff Calculator
Compare the snowball and avalanche debt payoff methods side by side. Add your debts, set a monthly extra-payment budget, and see exactly how long you'll be debt-free and how much interest each strategy costs.
Enter each debt's balance, APR and minimum monthly payment. Edit the example rows or add your own.
| Debt name | Balance | APR % | Min payment |
|---|
How to use
Snowball vs avalanche — the honest version
Avalanche (highest APR first) almost always saves you the same amount or more total interest than snowball (smallest balance first), because it targets the debt that's costing you the most every month. Snowball's real advantage isn't math — it's momentum: clearing a whole debt quickly gives many people the motivation to stick with the plan. Pick whichever you'll actually follow through on.
Why extra payments compound your timeline
Every pound above the minimum goes straight to principal instead of future interest, so it shrinks the balance interest is calculated on every single month afterwards. That's why doubling your extra budget rarely just halves your payoff time — it often cuts it by much more, especially on high-APR cards.
When minimums barely cover interest
If a minimum payment is close to (or below) the interest accruing that month, almost nothing goes toward the actual balance — you can pay for years and barely move it. In that situation, the size of your extra-payment budget is the single biggest lever you have; even a small increase can turn a debt that never shrinks into one with a real payoff date.
Frequently asked questions
What's the difference between snowball and avalanche?
Snowball pays off your smallest balance first, regardless of interest rate, then rolls that payment onto the next-smallest debt. Avalanche pays off your highest interest rate first, regardless of balance size. Snowball gives you faster "wins" — a debt disappears sooner, which keeps many people motivated. Avalanche is the mathematically optimal order because it attacks the interest that costs you the most first.
Which method saves more money?
Avalanche saves the same amount or more total interest than snowball, for the same monthly budget — it can never cost more, because it always targets the debt accruing interest fastest. The gap is usually small when your debts have similar rates, and larger when one debt has a much higher APR than the rest. Snowball is not a way to save money; it's a way to stay motivated.
What if I can't afford any extra payment?
Set your extra monthly budget to £0 and the calculator will show you the minimums-only payoff timeline. If a debt's minimum payment doesn't even cover the interest accruing on it each month, the balance will grow forever rather than shrink — the calculator flags this so you know that debt needs a higher payment or a lower rate (e.g. a balance transfer) before it can ever be cleared.
Does this include compound interest?
Yes. Each simulated month, interest is calculated on the current balance at your APR divided by 12, added to the balance, and only then is the payment applied — the standard way revolving credit and instalment loans actually compound. That interest-then-payment order is repeated every month of the simulation, so the totals reflect true compounding, not a simple estimate.