When is self-assessment due?

The tax year runs 6 April to 5 April. Paper returns are due by 31 October, online returns by 31 January following the tax year end. Payment is also due 31 January, with a second payment on account due 31 July.

What are payments on account?

If your tax bill exceeds £1,000 (and less than 80% was collected at source), HMRC requires advance payments towards next year's bill. Each payment on account is half the previous year's total tax. They are due 31 January and 31 July.

What expenses can tradespeople claim?

Allowable expenses include: materials and tools, vehicle costs (fuel or mileage), insurance, phone/broadband (business proportion), workwear and PPE, training, accountancy fees, advertising, and use of home as office (simplified: £6/week).

How does the personal allowance taper work?

For income over £100,000, your personal allowance reduces by £1 for every £2 above £100,000. This means the allowance is completely eliminated at £125,140 income, creating an effective 60% tax rate in this band.

Do I need to register for self-assessment?

You must register with HMRC if your self-employed income exceeds £1,000 in a tax year. Register by 5 October following the tax year you need to file for. You can register online through the HMRC website.

What is the NI Class 2 and Class 4 difference?

Class 2 is a flat weekly rate (around £3.45/week) paid by all self-employed with profits above the small profits threshold. Class 4 is a percentage of profits: 6% on profits between £12,570-£50,270, and 2% on profits above £50,270.

TradeCalculator

Self Assessment Tax Calculator

Estimate your self-assessment tax bill as a UK tradesperson

Annual Turnover

Allowable Expenses

How We Calculate This

Enter your business turnover and allowable expenses to calculate profit. The calculator applies the personal allowance (tapered above £100,000), then calculates income tax across all bands. National Insurance Class 2 (flat rate) and Class 4 (percentage of profits) are added, along with any student loan repayments. The result shows your total tax bill, take-home pay, effective tax rate, and payments on account.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.