How to Calculate Self-Employed Tax in the UK: Step-by-Step Guide

Introduction

Tax in the UK is worked out in layers: allowances first, then bands, then separate charges such as National Insurance and student loans. Once you see each layer, the numbers on your payslip stop being a mystery.

This guide explains how to calculate self-Employed Tax in the UK, step by step. Estimate income tax and Class 4 National Insurance on your sole trader profits. You'll see the formula, a fully worked example and practical tips for UK readers.

What this calculation covers

Estimate income tax and Class 4 National Insurance on your sole trader profits.

Knowing your figures helps you check your payslip, negotiate pay, plan pension contributions and avoid a surprise bill from HMRC. Mistakes in tax codes are common, and HMRC will only refund what you notice and claim.

The method and formula

Income tax is charged on profit above your personal allowance. Class 4 NI is 6% on profits between £12,570 and £50,270 and 2% above.

Every figure on our self-Employed Tax Calculator follows this method, so you can check the working yourself.

Worked example

Here's a typical example using these figures:

Running them through the method gives:

The headline figure is total tax and ni: £7,131.80. Change any input and the result will move with it.

How to use the calculator

1. Enter or choose annual profit (£).
2. Read your results. The main figure is shown at the top, with a breakdown underneath.
3. Try different values to compare scenarios side by side.

Tips for UK readers

• Check your tax code on every payslip. 1257L is the standard code for 2025/26; anything else deserves a quick look in your HMRC app.
• Pension contributions and salary sacrifice reduce your taxable pay, which matters most if you're near a band threshold.
• If your income is between £100,000 and £125,140, you lose personal allowance and face an effective 60% marginal rate. Pension contributions can bring it back.
• Keep records of expenses and allowances you can claim, such as working-from-home costs, professional fees and uniform cleaning.

Frequently asked questions

What's the quickest way to work out self-Employed Tax?

Use our free self-Employed Tax Calculator. It applies this method automatically: Income tax is charged on profit above your personal allowance. Class 4 NI is 6% on profits between £12,570 and £50,270 and 2% above.

When does the UK tax year start?

The UK tax year runs from 6 April to 5 April the following year. Most allowances and bands reset on 6 April.

Where can I check the official rates?

GOV.UK publishes all current income tax, National Insurance and student loan rates. Our figures are based on the tax year shown on each calculator.

Is this calculator a substitute for advice?

No. It gives a clear estimate for common situations. For complex cases such as multiple incomes, benefits in kind or residency questions, speak to an accountant or HMRC.

Summary

To work out self-Employed Tax, follow the method above: Income tax is charged on profit above your personal allowance. For a quick, accurate answer with your own figures, use the calculator.

Next, read Self-Employed Tax: Common Mistakes, Tips and FAQs.