Self Assessment Tax Calculator
Instantly estimate your UK Income Tax, Class 4 National Insurance, and total tax liability based on your self-employed income and allowable expenses.
Calculate Your Tax Liability
Enter your self-employment turnover, allowable expenses, and any other income to instantly see your estimated Income Tax, National Insurance, and take-home pay.
Tax Liability Estimator
Based on standard 2025/2026 UK tax bands and Personal Allowance rules.
How it Works
Understanding your tax calculation
Calculate Net Profit
We subtract your allowable business expenses from your total turnover to find your taxable self-employment profit.
Apply Personal Allowance
Your standard £12,570 tax-free allowance is deducted from your total income. This allowance tapers for incomes over £100,000.
Apply Tax Bands
Remaining taxable income is taxed at 20% (Basic), 40% (Higher), or 45% (Additional) depending on the thresholds.
Add National Insurance
Class 4 NI is calculated on your net profits: 6% on profits between £12,570 and £50,270, and 2% on profits above this.
UK Tax Bands & Rates
A general overview of the Income Tax and Class 4 National Insurance thresholds used in this estimation.
| Tax Type | Band / Threshold | Rate |
|---|---|---|
| Personal Allowance | Up to £12,570 | 0% |
| Basic Rate Income Tax | £12,571 to £50,270 | 20% |
| Higher Rate Income Tax | £50,271 to £125,140 | 40% |
| Additional Rate Income Tax | Over £125,140 | 45% |
| Class 4 National Insurance | £12,570 to £50,270 | 6% |
| Class 4 National Insurance | Over £50,270 | 2% |
Self Assessment FAQ
Answers to the most frequently asked questions about UK Self Assessment, allowable expenses, and tax deadlines.
A Self Assessment tax return is a form used by HMRC to calculate how much Income Tax and National Insurance you owe on your earnings, particularly if you are self-employed, a company director, or have other untaxed income such as rental property or dividends.
Allowable expenses are the everyday costs of running your business, such as office supplies, travel costs, clothing, staff costs, and things you buy to sell on. These are deducted from your total turnover to calculate your taxable profit, lowering your tax bill.
The deadline for filing a paper Self Assessment tax return is 31 October following the end of the tax year. The deadline for filing online and paying any tax owed is 31 January of the following year.
The standard Personal Allowance is £12,570. However, if your total adjusted net income exceeds £100,000, your Personal Allowance is reduced by £1 for every £2 earned above this threshold. This means the allowance is fully eliminated once income reaches £125,140, creating an effective 60% tax rate in this band.