Self Assessment tax-shock estimator

This tool assumes:

• 2025-26 England, Wales & NI bands: personal allowance £12,570; basic rate 20% to £50,270; higher rate 40% to £125,140; additional rate 45%. Personal allowance tapers £1 for every £2 over £100,000.
• Class 4 National Insurance: 6% between £12,570 and £50,270, then 2% above. Class 2 is voluntary below the £6,845 Small Profits Threshold.
• Payments on account apply when your bill is over £1,000 and less than 80% was collected at source — each is 50% of the previous year's bill.
• Student loan repayments are added at 9% (Plans 1/2/4/5) or 6% (Postgrad) above the relevant threshold.
• Scottish income tax bands differ — this tool uses England/Wales/NI rates.

Primary sources:

• HMRC: Rates and allowances for Income Tax
• HMRC: Self Assessment tax returns
• HMRC: Understand your Self Assessment tax bill (Payments on account)
• HMRC: Self-employed National Insurance rates
• HMRC: Repaying your student loan