About this calculator
Avalanche vs Snowball is a free, no-login UK debt payoff calculator. Enter your debts — credit cards, store cards, personal loans, overdrafts — and it shows you side by side how much interest you'd pay and how long it would take using the debt avalanche method versus the debt snowball method. The goal is to give you accurate numbers so you can make an informed choice, with no upselling and no data collection.
Who built this
Why we built it
Most debt calculators we found were either US-focused (wrong currency, wrong regulatory context), cluttered with ads, or required you to create an account before showing you anything useful. We wanted a clean, fast tool built specifically for UK credit cards and personal loans that anyone could use in under two minutes — no sign-up, nothing to install, nothing sold to you.
We also wanted the blog articles to be genuinely useful: worked examples with real UK APRs, honest comparisons of both methods, and explanations of why the maths works the way it does. The main comparison is Debt Avalanche vs Snowball: Which Saves More Money in the UK? — it includes our original data from analysing 1,000 simulated UK debt scenarios.
How the calculator works
The calculator uses standard monthly compound interest arithmetic — the same maths your credit card issuer uses. Here is the exact logic applied each month:
Apply monthly interest to every open balance. Your annual APR is divided by 12 and applied to the current balance — so a £2,000 balance at 22.9% APR accrues approximately £38.17 in interest in month one.
Subtract the minimum payment from every debt. Minimums are fixed at whatever you enter — the calculator does not recalculate them as balances fall, because many UK borrowers are on fixed minimum arrangements or prefer to model a consistent payment. If your card recalculates minimums, the calculator will be slightly conservative (real interest paid will be lower).
Apply the extra payment to the priority debt: for avalanche this is the highest-APR debt; for snowball it is the smallest balance. The full extra payment goes to one target — not split across debts.
When a debt reaches zero, its full previous payment (minimum + any extra that was directed to it) automatically rolls onto the next priority debt. This "payment roll" compounds your speed over time — the avalanche or snowball accelerates as each debt falls.
Continue until all balances are zero. The simulation is capped at 600 months (50 years) to prevent infinite loops if a minimum payment is smaller than the monthly interest charge — a warning is shown if this happens.
All calculations happen locally in your browser. No balance, APR, or personal information is ever sent to our servers or stored anywhere. The URL updates as you enter debts so you can bookmark or share a specific scenario, but that data stays in the URL — it is never logged.
Accuracy commitments
We take accuracy seriously because the purpose of this tool is to help people make real financial decisions. Here is what we do and do not model:
The calculator was stress-tested against the 1,000 scenario simulation and its month-by-month results match the hand-calculated figures in the £10,000 worked example article. If you spot an error, please email us and we will verify and fix it within 48 hours.
Our content standards
Every article on this site is written to explain real UK debt concepts using realistic APRs and actual regulation (FCA, not SEC). We use UK-specific rates: credit card APRs in the 18–30% range, overdraft EARs in the 19–40% range, and personal loan APRs in the 6–25% range. We link to the FCA consumer credit register, MoneyHelper, and other authoritative UK sources where relevant.
We aim to update articles when APR norms or regulatory guidance changes. If you find an article that references outdated rates or regulations, please let us know.
What we are (and are not)
This is an educational tool, not regulated financial advice. The calculator is accurate for the inputs you provide, but your actual payoff will depend on factors it does not model: whether your minimum payment changes as your balance falls, any payment holidays, charges, or balance transfers you make along the way, and changes to your interest rate (for example, if a 0% promotional period ends).
We are not a debt advice charity, a lender, or a regulated financial adviser. If you are struggling with debt — missing payments, feeling stressed about money, or simply unsure where to start — please contact one of the free UK debt advice services below. They are staffed by trained advisers, completely free to use, and authorised by the Financial Conduct Authority.
Free UK debt advice — regulated and independent
- MoneyHelper — Debt advice Run by the Money and Pensions Service, a government-backed body. Impartial guidance and referrals to free debt advice services. Also runs the Debt Advice Locator to find local help.
- StepChange Debt Charity Free debt advice by phone or online. Can arrange debt management plans, Individual Voluntary Arrangements (IVAs), and other formal solutions. FCA-authorised.
- Citizens Advice — Debt and money Free, confidential advice in person, online, or by phone. Available across England and Wales. No appointment needed for online help.
- National Debtline Free helpline and self-help resources. Covers England, Wales, and Scotland. Specialists in helping people handle their own debt without a debt management plan if that is the right route.
- PayPlan Free debt advice and debt management plans, funded by creditors (not you). FCA-regulated. Good option if you have multiple creditors and need a structured plan.
Affiliate disclosure
Some articles on this site contain affiliate links — for example, links to 0% balance transfer credit cards. If you apply for a product through one of those links, we may receive a commission from the lender at no extra cost to you. We only link to products where they are genuinely relevant to the topic being discussed, and our editorial content is not influenced by any commercial relationships. The calculator itself is, and will always remain, completely free with no advertising embedded in it.
Any page containing an affiliate link is clearly marked. We do not accept payment for editorial mentions or rankings, and we do not compare products outside of editorial context.
Corrections and feedback
If you spot a calculation error, a broken link, an article that references outdated rates, or anything else that seems wrong, please let us know at hello@avalanchevssnowball.co.uk. We read every message and fix errors within 48 hours. We cannot offer personal debt advice — for that please use the regulated resources above — but we take accuracy very seriously and genuinely want to know if something is wrong.