BriskCal

Debt payoff calculator

On the example below, the avalanche costs £156 less in interest than the snowball. The snowball clears its first debt in month 3, against month 13. Both clear everything in about 2 years. Change the figures for your own.

DebtBalanceRateMinimum
Avalanche £1,922 interest · 2 years 1 month
Snowball £2,078 interest · 2 years 1 month

The avalanche costs £156 less in interest. The snowball clears its first debt in month 3, against month 13 for the avalanche.

Avalanche order

  1. Credit card month 13 £562.87 interest
  2. Interest-free purchase plan month 20 £0.00 interest
  3. Car finance month 25 £1,359.00 interest

Snowball order

  1. Interest-free purchase plan month 3 £0.00 interest
  2. Credit card month 14 £691.31 interest
  3. Car finance month 25 £1,387.05 interest

How this is worked out

Each month, interest is added to every outstanding balance, then every minimum payment is made, then whatever is left of your budget goes at a single target debt. When that debt clears, the money rolls straight on to the next one in the same month rather than waiting. The only difference between the two plans is how the target is chosen: smallest balance for the snowball, highest rate for the avalanche. Both are simulated month by month rather than solved, because the roll-over means each month depends on the one before it.

Two interest-free debts of £300 and £700, minimums of £50 each, £200 a month available

  1. Month 1: both £50 minimums are paid, and the spare £100 goes at the £300 debt — leaving £150 and £650.
  2. Month 2: the same again clears the smaller debt, leaving £600 on the larger one.
  3. Month 3 onwards: the freed-up £50 joins the budget, so the whole £200 attacks what is left.
  4. The larger debt clears in month 5. £1,000 paid in total, and no interest, because both rates were zero.

That example is deliberately interest-free so the arithmetic can be followed on paper. A test recomputes it on every build, so if the engine ever stopped agreeing with what is written here, the build would fail.

Why there is nothing to cite here

Like the mortgage overpayment calculator, this works entirely from what you type — there is no published rate to look up, so nothing to go out of date and no external source to lean on. It shows its method instead.

What catches people out

  • The avalanche always costs less interest when your debts are at different rates — that is arithmetic, not opinion, and this site tests it across hundreds of generated cases. What it does not tell you is which method you will actually stick to, and a plan abandoned in month four is worse than a slightly more expensive one finished.
  • When every debt is at the same rate the two methods are equivalent. There is no cheaper order to find, so the choice is purely about which one keeps you going.
  • Both methods depend on rolling payments forward. When a debt clears, its minimum payment does not become spending money — it joins the amount attacking the next debt. That roll-over is where almost all of the speed comes from, and skipping it turns either method into simply paying minimums.
  • A 0% balance transfer changes the answer completely, and this calculator cannot see the end of the promotional period. If a card reverts to 24% in eight months, the avalanche will currently rank it last and be wrong from month nine. Enter the rate you expect to be paying, not today's teaser.
  • Minimum payments on credit cards usually fall as the balance falls, typically to a percentage of the balance or a floor of a few pounds. This treats the minimum as fixed, which is slightly conservative — a real card would free up a little more each month.
  • If the monthly amount does not cover the interest, no ordering saves you. The calculator says so rather than producing a sixty-year plan, because at that point the arithmetic is not the problem and free debt advice is the right next step.

If the payments are not affordable at all, arithmetic is not what is needed. Free, independent advice is available from StepChange, Citizens Advice and National Debtline. None of them charges.

Questions

What is the difference between snowball and avalanche?

Both pay every minimum every month and throw whatever is left at one debt. They differ only in which one. The snowball attacks the smallest balance, so individual debts disappear sooner. The avalanche attacks the highest interest rate, so less interest is charged overall.

The calculator runs both against your actual figures and shows the difference in months and in pounds, which is usually a more useful basis for choosing than either name.

Which one should I use?

This site does not answer that, and not out of caution — it genuinely depends on something the arithmetic cannot see. The avalanche costs less. Whether the first cleared card arriving three months sooner is what keeps you going is a question about you.

What the numbers can tell you is the size of the trade-off. If the avalanche saves £40 across two years, the difference is small enough to choose on motivation. If it saves £900, that is worth knowing before deciding.

What if I cannot cover the minimum payments?

Then this calculator is the wrong tool, and it will say so rather than produce a plan. Free, independent debt advice is available from StepChange, Citizens Advice and National Debtline. None of them charges, and all of them can do things a spreadsheet cannot, including negotiating with creditors.

Does this include my mortgage?

It can, but it usually should not. A mortgage is secured, long-term and typically at a far lower rate than consumer debt, so putting it in the same list tends to swamp the comparison. The mortgage overpayment calculator is the better tool for that question.