United Kingdom  ·  2026

Your January bill is about 150% of what you saved for.

The demand that lands on 31 January is not last year's tax. It is last year's balance plus half of next year's estimate, with the other half due in July. A first full year of self-employment therefore produces a bill half as large again as the figure you had been putting aside — and it is entirely predictable, which is why it is worth knowing in advance rather than in January.

Payments on account

Once your bill passes £1,000, HMRC asks for half of next year up front in January and the other half in July. Nothing has gone wrong; this is simply how the system works, and it catches almost everybody once.

Class 4 National Insurance

6% on profit between £12,570 and £50,270, then 2% above. It sits on top of income tax and is charged on your profit rather than your household income.

The 60% band

Between £100,000 and £125,140 the personal allowance is withdrawn at £1 for every £2 earned. Each extra pound is taxed at 40% and drags 50p of allowance into the 40% band with it — an effective 60% rate that appears on no rate card.

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What this does not cover. Scottish rates differ and are not applied. Student loan repayments, pension relief and capital allowances are not modelled.

Track it all year

The calculator answers today. The app remembers, watches every invoice, and in December tells you what you forgot to claim.

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