UK Self-Employed Tax and National Insurance Calculator 2026/27
Estimate sole-trader taxable profit, Income Tax, Class 4 National Insurance and payments on account.
What this calculator explains
Self-employed tax is based on profit rather than turnover. The calculator separates business receipts from allowable expenses, combines the resulting profit with other taxable income and then estimates Income Tax and Class 4 National Insurance separately.
The result shows liability before and after tax already paid. Payments on account are presented as a cash-flow requirement rather than extra tax, with a clear explanation of when the amount due may include an advance towards the following year.
How the estimate is calculated
- Subtract entered allowable expenses from turnover to estimate business profit.
- Combine profit with entered non-business income and apply applicable adjustments.
- Calculate Income Tax using the selected jurisdiction and 2026/27 bands.
- Calculate Class 4 National Insurance using current profit thresholds and rates.
- Add selected student-loan Self Assessment deductions where supported.
- Subtract PAYE and prior payments, then show liability and an indicative cash-flow reserve.
Formula
Business profit = turnover − allowable business expenses; total estimate then adds Income Tax and Class 4 National Insurance after applicable allowances
Worked example
A sole trader has £70,000 turnover and £15,000 allowable expenses, giving £55,000 profit. In a simplified rest-of-UK example with no other income, taxable income after a £12,570 allowance is £42,430. Illustrative Income Tax is £9,432, while Class 4 National Insurance is about £2,356.60 using 6% between £12,570 and £50,270 and 2% above. The combined illustration is £11,788.60 before tax already paid, student loans or other adjustments.
Current rules and configuration notes
- Self-employed Income Tax and Class 4 National Insurance are based on profit after allowable expenses, not turnover.
- For 2026/27, Class 4 National Insurance is 6% on profits from £12,570 to £50,270 and 2% above £50,270.
- Payments on account affect cash timing and must be shown separately from the underlying liability.
Update requirement: Review tax bands, allowances, Class 4 thresholds/rates, student-loan rules and payment guidance each tax year.
Included in the estimate
- Turnover and allowable-expense inputs
- Income Tax and Class 4 National Insurance
- Other income and selected adjustments
- Tax already paid
- Indicative payments-on-account view
- Monthly tax-reserve target
Not included or not guaranteed
- Corporation Tax or limited-company salary/dividend planning
- VAT returns and Making Tax Digital submissions
- Capital gains and complex loss relief
- A legal decision that an expense is allowable
- Preparation or filing of Self Assessment
Frequently asked questions
Is self-employed tax based on turnover?
No. Income Tax and Class 4 National Insurance are generally based on taxable profit after allowable expenses, not total sales.
What counts as an allowable expense?
The expense must meet HMRC rules and relate to the business. Mixed personal and business costs may need an appropriate business proportion.
What are payments on account?
They are advance payments towards the next Self Assessment bill, normally based on the prior year. They affect cash due but do not create a second layer of tax.
Does Class 2 National Insurance still apply?
Current rules can create voluntary or special Class 2 situations. The result identifies the selected tax-year treatment and does not add one universal compulsory amount.
Can I include employment income?
Yes. Other income can use some or all of the Personal Allowance and tax bands, changing the tax on business profit.
Does this work for a limited company?
No. A company and its owner have separate Corporation Tax, payroll and dividend considerations that need another model.
Official sources
- GOV.UK — Income Tax rates and Personal Allowances
- GOV.UK — National Insurance rates and allowances
- GOV.UK — Estimate your Income Tax for the current year
Applicable period: 2026-04-06/2027-04-05 · Last reviewed: September 3, 2026
Recommended internal links
Create a tax reserve before the deadline
Save the projection and track tax already paid so the reserve target reflects the remaining estimated liability.
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