Debt Payoff Calculator

Snowball vs avalanche: how the two strategies actually differ

The avalanche method targets the debt with the highest interest rate first, regardless of balance. Every extra pound you throw at debt goes to whatever is costing you the most in interest. Mathematically, this always wins. It clears your debts for the lowest total interest paid, every time.

The snowball method targets the smallest balance first, regardless of rate. The maths is worse, sometimes by hundreds of pounds. The behaviour is better. Closing accounts one by one gives you visible wins, and visible wins are what keep most people paying down debt for the 18 to 36 months it usually takes.

Here is the surprising bit. The avalanche almost always saves more interest in total, but the snowball typically clears more individual debts in the first 12 months. If you have five debts and one is a £400 store card at 26%, the avalanche kills it first because the rate is highest. But if your smallest debt is a £400 personal loan at 7%, the avalanche would ignore it for two years while the snowball would close it in three months. Most people quit debt repayment because progress feels invisible, not because the maths is wrong. The strategy you finish beats the one that is £200 cheaper on paper.

When each method wins

Pick the avalanche if your rates vary a lot (say, a 26% store card sitting next to a 6% car loan), if you have already paid down debt successfully before, or if your total balance is large enough that a few hundred pounds of interest savings matters.

Pick the snowball if your rates are all within a narrow band (say, three cards all between 18% and 23%), if you have tried and failed to clear debt before because progress felt invisible, or if one of your small debts is causing relationship stress (a Klarna account, a loan from a family member). The interest cost of the snowball over the avalanche in that scenario is usually under £150, which is a small price to pay for actually finishing.

The single most important number on the page is not the strategy. It is the extra monthly payment field. The gap between paying minimums and paying minimums plus £100 a month on a typical UK debt mix is measured in years and thousands of pounds. Whether you pick snowball or avalanche matters less than whether the extra payment exists at all. If you can also build a buffer alongside, the emergency fund calculator shows how much cash to keep accessible so a single unexpected bill does not send you back to the credit card.

A worked example

Three debts, an extra £150 a month on top of minimums:

• Credit card: £4,000 at 22% APR, minimum payment £100
• Personal loan: £8,000 at 8% APR, minimum payment £200
• Store card: £1,200 at 26% APR, minimum payment £40

With the avalanche, the extra £150 attacks the store card first (highest rate at 26%), then the credit card (22%), then the personal loan (8%). All three clear in roughly 30 months at a total interest cost of around £1,650.

With the snowball, the extra £150 attacks the store card first (smallest balance), then the credit card, then the personal loan. In this case the order matches the avalanche because the store card is both the smallest and the highest-rate debt. Both strategies finish at the same time.

Flip the example so the personal loan is the smallest debt and the snowball will attack the lowest-rate debt first while the avalanche keeps hammering the credit card. In that scenario, the avalanche typically saves £400 to £800 in interest and finishes one to three months earlier.

UK priority debts: when the calculator's advice does not apply

Neither snowball nor avalanche knows the difference between a credit card and a council tax arrears notice. They should. In the UK, certain debts carry powers that consumer debts do not, and those debts always come first regardless of interest rate or balance. These are called priority debts and missing them can mean bailiffs, disconnected utilities, or even loss of your home.

Priority debts include:

• Mortgage or rent arrears (loss of home)
• Council tax arrears (bailiffs, attachment of earnings)
• Gas, electricity, and water arrears (disconnection, prepayment meter)
• Magistrates' court fines and TV licence fines
• HMRC tax arrears (direct collection from earnings or bank accounts)
• Child maintenance arrears via the Child Maintenance Service

Clear or negotiate these first, no matter what your credit card APR looks like. The calculator is built for the non-priority pile: credit cards, store cards, BNPL balances, personal loans, overdrafts. If you have priority arrears as well, treat the calculator as a tool for the consumer debt portion only, and ringfence the priority debts in a separate plan. gov.uk's debt options guide explains the legal differences in more detail.

FCA-regulated lenders (credit card issuers, personal loan providers, BNPL firms covered by consumer credit rules) are subject to forbearance rules. If you cannot make a minimum payment, you have a legal right to ask for a payment plan, an interest freeze, or a breathing space. Lenders are required to treat customers in financial difficulty fairly. Use that right. Calling and asking for a 30-day breathing space is not a black mark, it is a protected option, and lenders would rather negotiate than send a default to your credit file.

When to stop using a calculator and get free debt advice

This calculator is for people who can clear their debts on their current income with discipline and an extra monthly payment. If the maths does not add up to debt-free within a reasonable timeframe (say, five years on a typical balance), or if you cannot afford the minimum payments, the answer is not a better spreadsheet. It is free, confidential debt advice from a regulated charity. None of these services charge a fee. All of them are worth using before paying any commercial debt-management company.

• StepChange - the UK's largest free debt charity. Online debt remedy tool, full advice over the phone, help setting up a Debt Management Plan or an IVA if appropriate.
• Citizens Advice - free face-to-face and phone advice on debt, benefits, and creditor negotiation. Useful if your situation involves priority debts, benefit issues, or court action.
• National Debtline - run by the Money Advice Trust. Free phone and webchat advice, with a self-help pack and template letters for negotiating with creditors.
• MoneyHelper - the government-backed service that signposts to the above and runs its own debt advice locator.

Our UK debt help guide walks through when each of these is the right call, what a Debt Management Plan actually looks like in practice, and the cases where an IVA or bankruptcy is the honest answer. Avoid any company that charges a fee to "consolidate" or "manage" your debts. Everything they offer is available free.

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