Tax calculators
Self-Employed Tax Calculator
Estimate the Income Tax and Class 4 National Insurance due on your sole trader profits, and see how much is worth setting aside each month.
Estimated tax and National Insurance
£7,132
on £40,000 of profit
Suggested reserve: £594 per month
Annual summary
- Taxable profit
- £40,000
- Income Tax
- £5,486
- Class 4 National Insurance
- £1,646
- Total estimated liability
- £7,132
- Estimated income after tax
- £32,868
- Monthly equivalent after tax
- £2,739
- Effective tax rate
- 17.8%
Income Tax band by band
| Band | Rate | Amount | Tax |
|---|---|---|---|
| Basic rate | 20.00% | £27,430.00 | £5,486.00 |
Class 4 National Insurance band by band
| Band | Rate | Amount | Tax |
|---|---|---|---|
| Profits between £12,570 and £50,270 | 6.00% | £27,430.00 | £1,645.80 |
Where your profit goes
- Income after tax — £32,868 (82%)
- Income Tax — £5,486 (14%)
- Class 4 NIC — £1,646 (4%)
These calculations are estimates based on the information entered and the tax rates and assumptions shown. They are intended as a general guide and do not constitute tax advice. Your actual tax position may differ depending on your circumstances, reliefs, other income and applicable tax rules.
About this tool
What the self-employed tax calculator does
This calculator estimates what a sole trader or partner owes on their trading profits: Income Tax through the normal bands, plus Class 4 National Insurance, which is charged on profits rather than on earnings. It then shows the income left over and a suggested monthly reserve.
It is a genuinely separate calculation from the employee salary calculator. Employees pay Class 1 National Insurance at different rates and thresholds, so running a profit figure through a salary tool gives the wrong answer.
Method
How the calculation works
If you enter turnover and expenses, the calculator treats the difference as estimated taxable profit. That is an estimate: real taxable profit may need adjustments for disallowable costs, capital allowances, private use and the basis period rules.
Profit and any other income are added together and the Personal Allowance is set against the total. The remainder runs through the basic, higher and additional rate bands.
Class 4 National Insurance for 2026/27 is charged at 6% on profits between £12,570 and £50,270, and 2% above that. Class 2 is treated as paid where profits exceed £7,105, and is otherwise voluntary at £3.65 a week.
Worked example
A £45,000 profit in 2026/27
On profits of £45,000, the Personal Allowance of £12,570 leaves £32,430 of taxable income, all within the basic rate band, so Income Tax is £6,486.
Class 4 National Insurance is charged at 6% on the £32,430 of profit between £12,570 and £45,000, which is £1,945.80.
The total estimated liability is £8,431.80, leaving £36,568.20 — around £702 a month worth reserving for tax.
Assumptions
What this calculator assumes
It assumes a full tax year of self-employment, profits taxed in England, Wales or Northern Ireland, no payments on account already made, no losses brought forward, no Child Benefit charge and no tax deducted at source. Construction subcontractors with CIS deductions should treat the result as the liability before those deductions are credited.
Keeping the underlying figures reliable is the hard part. Our bookkeeping service keeps records current through the year, and Self Assessment turns them into a filed return.
Rates and assumptions
What this calculator uses
- Tax year shown
- 2026/27
- Geographical scope
- England, Wales and Northern Ireland
- Rates last reviewed
- 19 September 2026
- Source of rates
- HMRC / GOV.UK
Official guidance
- Self-employed National Insurance rates (GOV.UK)
- Income Tax rates and Personal Allowances (GOV.UK)
- Expenses if you're self-employed (GOV.UK)
- Self Assessment tax returns (GOV.UK)
These calculations are estimates based on the information entered and the tax rates and assumptions shown. They are intended as a general guide and do not constitute tax advice. Your actual tax position may differ depending on your circumstances, reliefs, other income and applicable tax rules.
Questions
Common questions
No. This is the tax and Class 4 National Insurance on the profit you enter. Your actual payment to HMRC also reflects payments on account already made, the balancing payment for the previous year, tax deducted at source such as CIS, other income, and any reliefs claimed.
Need help with Self Assessment?
We prepare sole trader accounts and Self Assessment returns for clients across Scunthorpe and North Lincolnshire, with the tax position explained before anything is filed.
Related services
Services that work alongside this
- Explore bookkeeping
Accurate, reconciled records kept up to date weekly or monthly, so VAT, payroll and year-end all take care of themselves.
- Explore self assessment tax returns
Returns prepared and filed for sole traders, directors, landlords and higher earners — early, accurate and with the reliefs claimed.