Self-Employed Tax Calculator UK 2025/26

How Self-Employed Tax Works in the UK

When you work for yourself in the United Kingdom, you are responsible for calculating and paying your own tax through HMRC's Self Assessment system. Unlike employees, who have tax deducted automatically through PAYE, self-employed individuals must file an annual tax return and settle their bill directly.

Your tax is calculated on your taxable profit, which is your total business income (turnover) minus allowable business expenses. This profit figure is then used to work out both income tax and Class 4 National Insurance contributions. For the 2025/26 tax year, the personal allowance is £12,570, meaning you only pay income tax on profits above this amount.

Income tax is charged in bands: the basic rate of 20% applies to taxable income between £12,571 and £50,270, the higher rate of 40% applies between £50,271 and £125,140, and the additional rate of 45% applies above £125,140. If your income exceeds £100,000, your personal allowance is reduced by £1 for every £2 of income over that threshold, effectively creating a 60% marginal rate in that band.

Class 4 National Insurance is an additional charge for the self-employed. For 2025/26, you pay 6% on profits between £12,570 and £50,270, and 2% on any profits above £50,270. Together with income tax, these make up the bulk of your self-employed tax liability.

What Counts as Allowable Expenses?

HMRC allows you to deduct business expenses that are incurred “wholly and exclusively” for business purposes. Reducing your taxable profit with legitimate expenses can make a significant difference to your tax bill. Common allowable expense categories include:

• Office and premises costs — rent, rates, power, insurance, and a proportion of home costs if you work from home
• Travel and subsistence — business mileage, public transport, parking, and meals on overnight business trips
• Staff and subcontractors — wages, freelancer fees, and employer National Insurance contributions
• Equipment and supplies — computers, software, stationery, tools, and raw materials
• Professional fees — accountancy, legal advice, professional body subscriptions, and trade memberships
• Marketing and advertising — website hosting, domain names, online advertising, business cards, and printed materials
• Financial costs — bank charges, interest on business loans, credit card fees, and bad debts
• Phone and broadband — the business proportion of phone bills, broadband, and mobile contracts
• Insurance — professional indemnity, public liability, and business contents insurance
• Training — courses and qualifications directly related to your existing trade

You cannot claim for personal spending, clothing (unless protective or a uniform), fines or penalties, entertaining clients, or the initial cost of buying a business. If an expense has both personal and business use, you may only claim the business proportion. Always keep receipts and records to support your claims.

Example Self-Employed Tax Calculations

Freelancer earning £30,000 with £3,000 in expenses

Taxable profit: £27,000. After deducting the £12,570 personal allowance, £14,430 is taxable at the 20% basic rate, giving £2,886 in income tax. Class 4 NI on the profit between £12,570 and £27,000 is £865.80. Total tax bill: approximately £3,752. Take-home profit: roughly £23,248.

Sole trader earning £60,000 with £8,000 in expenses

Taxable profit: £52,000. Income tax is charged at 20% on the first £37,700 above the personal allowance (£7,540) and 40% on the remaining £1,730, giving roughly £8,232. Class 4 NI: 6% on £37,700 plus 2% on £1,730 comes to about £2,296.60. Total tax: around £10,529. Take-home profit: approximately £41,471.

Contractor earning £120,000 with £15,000 in expenses

Taxable profit: £105,000. With income over £100,000 the personal allowance starts to taper, reducing to £10,070. Income tax spans the basic and higher rate bands, producing a substantial bill. Class 4 NI adds a further charge on profits above £50,270 at the 2% rate. The total tax liability in this scenario is likely to exceed £30,000, leaving a take-home profit of around £72,000 to £75,000. At higher income levels, speaking to an accountant is especially important.

Key Dates for Self-Assessment

Missing a deadline can result in automatic penalties, so it is important to know the key dates in the Self Assessment calendar for the 2025/26 tax year:

• 5 October 2026 — deadline to register for Self Assessment if you became self-employed in the 2025/26 tax year
• 31 October 2026 — deadline for submitting a paper tax return (if not filing online)
• 31 January 2027 — deadline to file your online tax return and pay any tax owed for 2025/26, plus the first payment on account for 2026/27
• 31 July 2027 — second payment on account for 2026/27

Late filing incurs an immediate £100 penalty, with further charges accruing for each additional month of delay. Late payment attracts interest from the day after the deadline. HMRC may also charge penalties for inaccurate returns. Filing early does not mean paying early — you still have until 31 January to settle your bill — but it does give you more time to plan.