Self-employed tax and Class 4 National Insurance
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Sole traders are generally taxed on trading profit, not on every pound paid into a business bank account. Profit starts with income from the trade and deducts allowable costs under the applicable rules. Personal Income Tax and self-employed National Insurance are then considered on that profit alongside other income.
This guide focuses on the sequence rather than a single headline rate. For the 2026/27 tax year, check the current GOV.UK rules before filing or setting aside a final amount. Trading-allowance choices, losses and other income can change the outcome substantially.
Find the trade’s taxable profit
Keep records of sales, invoices and allowable business expenditure. A receipt for a cost is not enough on its own: it must qualify under the rules for your trade and chosen accounting basis. Where something is used partly privately, only the appropriate business share is normally relevant. Drawings paid to yourself do not automatically become a deductible business expense.
The trading allowance offers a simplified alternative in some cases, but you cannot ordinarily deduct both the full allowance and the same underlying costs. Compare the permitted approaches before entering expenses in a calculator. If you have several trades or an unusual accounting period, seek guidance on how those amounts are combined and reported.
Calculate Income Tax with other income
Trading profit may share your available Personal Allowance with salary, pension income or other taxable receipts. Add taxable sources as the relevant rules require, then allocate taxable amounts across Income Tax bands. Scottish taxpayers can have different non-savings Income Tax bands from taxpayers in England and Northern Ireland. A calculator that only receives trading profit cannot know every source of income.
A trading loss is not the same as a negative tax bill. Relief can be subject to conditions, time limits and the chosen claim. If you are newly self-employed or have stopped trading, the accounting year and the tax year can interact in ways a simple annual estimate cannot show. Keep documentary support for costs and any relief claimed.
Class 4 NI is a separate calculation
Class 4 National Insurance is generally charged on self-employed profits within the relevant thresholds. It is not employee Class 1 NI, which applies to employed earnings. A person who has both a job and a trade can have employment NI on wages and Class 4 on trading profit. The interaction of maximum contributions or special circumstances may require individual attention.
Do not take an employee payslip NI amount and apply its percentage to the whole trading profit. Look up current self-employed NI rates and thresholds on GOV.UK. Eligibility for National Insurance credits and voluntary contributions is a related but different question from whether Class 4 is due on a given level of profit.
Plan cash flow for Self Assessment
Unlike PAYE wages, tax on sole-trader profits is not necessarily withheld every time a customer pays an invoice. Reserve cash as sales arrive and update the estimate when expenses or other income change. Payments on account can bring forward cash payments based on a prior bill; they are not an extra tax on the same income.
Record the deadline shown for your own return and payment and check any payments on account. A forecast set-aside should be reviewed after significant changes such as a new job, higher profits or a pension contribution. The calculator estimates tax and a monthly reserve but cannot submit a return or decide that an expense is allowable.
Worked example: revenue is not profit
Suppose a sole trader invoices £50,000 during a trading year and has £12,000 of allowable business costs. The initial profit is £50,000 − £12,000 = £38,000. It would be wrong to calculate personal tax or Class 4 NI by treating the whole £50,000 as profit.
The £38,000 is not take-home cash: Income Tax and Class 4 NI may still apply, as might other adjustments. If the trader also earns wages, those earnings can affect the available income-tax bands. Enter the actual profit and other relevant details in the self-employed tax calculator; check current official thresholds before deciding how much cash to reserve.
Frequently asked questions
Do I pay tax on turnover or profit?
Usually on taxable trading profit, after the applicable treatment of allowable costs or the trading allowance.
Is Class 4 NI the same as employee NI?
No. Class 4 is generally assessed on self-employed profits; employee Class 1 relates to employment earnings.
Are payments on account extra tax?
They are advance payments towards a future Self Assessment bill, subject to the applicable rules.
Official sources
Check the linked official guidance for the latest figures before making a decision.
Related calculators
UK Calculators is independent and not affiliated with or endorsed by HMRC or any UK government body. These examples are illustrative, not personal tax, financial or legal advice.
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