Self Assessment Calculator UK 2026
Estimate Income Tax and Class 2/4 National Insurance on sole-trader trading profits. Includes the £1,000 trading allowance and rUK / Scotland Income Tax bands.
By Sammy S. · Founder · AuthorUpdated for 2026
Calculate Self Assessment tax
Enter turnover and expenses (or claim the trading allowance). Results update live.
Your inputs
Turnover, expenses, region
Total trading income before expenses
Enter allowable business expenses below.
e.g. employment — affects Income Tax bands / PA taper only
Total tax + NI
rUK£7,131.80
Effective 17.83% of trading profit £40,000
If payments on account apply, each instalment is usually half of last year’s Self Assessment bill (Income Tax + Class 4), due 31 January and 31 July. Planning estimate from this year’s figures: about £3,565.90 each. Confirm with HMRC.
Class 2 treated as paid (profits ≥ £7,105).
UK Self Assessment for sole traders is estimated for tax year 2026/27: trading profit after expenses or the £1,000 trading allowance, then Income Tax (rUK or Scotland) plus Class 2/4 National Insurance. Income tax uses the same HMRC bands as our UK salary engine; NI uses the self-employed Class 2/4 engine.
Worked example — £40,000
| Trading profit | £40,000.00 |
| Income Tax | £5,486.00 |
| Class 4 NI | £1,645.80 |
| Total tax + NI | £7,131.80 |
| Take-home from trading | £32,868.20 |
£40,000 profits → Income Tax £5,486.00 + NI £1,645.80 = £7,131.80
Formulas
- Trading profitProfit = Turnover − expenses OR Turnover − min(£1,000, Turnover) if claiming the trading allowance
- Income TaxTax on (trading profit + other income) after Personal Allowance (standard £12,570, taper above £100,000)
- Class 4 NI6% between LPL and UPL; 2% above UPL — on trading profit only
- Payments on account (simplified)Each instalment ≈ 50% of (Income Tax + Class 4) for planning — confirm HMRC rules
- Work out taxable trading profit — Use allowable expenses, or claim the £1,000 trading allowance instead (not both).
- Apply Income Tax bands — Other taxable income is added for banding and PA taper only.
- Add Class 2/4 NI — Same self-employed NI rules as the National Insurance calculator.
| Personal Allowance | £12,570 | gov.uk 2026/27 |
| Trading allowance | £1,000 | gov.uk trading allowance |
| Basic-rate band (rUK) | 20% to £50,270 | gov.uk Income Tax rates |
| Class 4 main / additional | 6% / 2% | Self-employed NI |
Key takeaways — Self Assessment
- Self Assessment for sole traders = Income Tax on profits + Class 2/4 NI (2026/27).
- £40,000 profits (rUK, no expenses) → about £7,131.80 total (£5,486.00 tax + £1,645.80 Class 4).
- Trading allowance of up to £1,000 can replace actual expenses when expenses are low.
- Class 4 starts above £12,570 at 6% (then 2%).
- Use Scotland mode for Revenue Scotland Income Tax bands.
Profit, Income Tax, and Class 4
Turnover − expenses or Turnover − £1,000 allowance
You cannot usually claim both the allowance and actual expenses
After £12,570 PA — 20% / 40% / 45% (rUK)
£40,000 profits → £5,486.00 Income Tax
6% then 2% on trading profit
£40,000 → £1,645.80 Class 4
What is Self Assessment for the self-employed?
Self Assessment is how HMRC collects Income Tax (and usually Class 2/4 National Insurance) from sole traders and others with income not fully taxed under PAYE.
For 2026/27, you typically report trading income after the end of the tax year, pay online, and may also make payments on account toward the next year.
Trading profit, expenses, and the £1,000 allowance
Taxable trading profit is turnover minus allowable expenses — or, if you claim the trading allowance, minus up to £1,000 instead of expenses.
If expenses are below £1,000, the trading allowance often gives a lower taxable profit. If expenses are higher, claim actual expenses.
Income Tax and Class 4 together
Example: £40,000 profit (no expenses, rUK) → Income Tax about £5,486.00 and Class 4 about £1,645.80, total £7,131.80.
At £60,000, higher-rate Income Tax applies — this model estimates £11,432.00 tax plus £2,456.60 Class 4 (total £13,888.60).
Thresholds and rates
| Tax year | 2026/27 |
| Personal Allowance | £12,570 |
| Trading allowance | £1,000 |
| Basic rate (rUK) | 20% to £50,270 |
| Higher rate (rUK) | 40% to £125,140 |
| Class 4 LPL | £12,570 |
| Class 4 rates | 6% / 2% |
Tax by profit level (rUK, £0 expenses)
| Profit | Income Tax | Class 4 | Total | Take-home |
|---|---|---|---|---|
| £20,000 | £1,486.00 | £445.80 | £1,931.80 | £18,068.20 |
| £30,000 | £3,486.00 | £1,045.80 | £4,531.80 | £25,468.20 |
| £40,000 | £5,486.00 | £1,645.80 | £7,131.80 | £32,868.20 |
| £50,000 | £7,486.00 | £2,245.80 | £9,731.80 | £40,268.20 |
| £60,000 | £11,432.00 | £2,456.60 | £13,888.60 | £46,111.40 |
| £80,000 | £19,432.00 | £2,856.60 | £22,288.60 | £57,711.40 |
| £100,000 | £27,432.00 | £3,256.60 | £30,688.60 | £69,311.40 |
Common mistakes
Who this helps
Checklist
- Register for Self Assessment if required and note the 31 January filing/payment deadline.
- Choose expenses vs the £1,000 trading allowance.
- Budget for Income Tax and Class 4 on profits.
- Plan payments on account (often 31 Jan and 31 Jul).
- Keep invoices and expense records.
- Use the NI-only tool if you only need Class 2/4.
Popular profit levels
Self Assessment calculator FAQ
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