Self Assessment Tax Calculator (2026/27)
For sole traders. Income Tax, Class 4 & Class 2 National Insurance, and your payments on account — no button, results update as you type.
Total turnover before expenses. Self-employment trading profit only — no separate PAYE job, savings, dividends, property income or capital gains modeled.
We automatically use whichever is better for you: your actual expenses, or the £1,000 trading allowance.
Self Assessment Tax Calculator (2026/27)
This calculator estimates your 2026/27 Self Assessment tax bill as a sole trader — the tax year running from 6 April 2026 to 5 April 2027. Enter your trading income and the numbers update immediately. It works out Income Tax (using the same rUK or Scottish bands as an employee), Class 4 and Class 2 National Insurance, automatically picks whichever is better for you between the £1,000 trading allowance and your actual expenses, and projects your payments on account — the January/July advance payments that catch a lot of first-time filers off guard.
Two Separate Taxes on the Same Profit
Self-employment profit is taxed twice, by two genuinely independent calculations. Income Tax works exactly like an employee’s: your £12,570 Personal Allowance (tapered above £100,000 adjusted net income), then 20/40/45% in England, Wales and Northern Ireland, or the six Scottish bands from 19% to 48%. Class 4 National Insurance is calculated completely separately, directly on your trading profit: 6% on profit between £12,570 and £50,270, and 2% above that — with no Personal Allowance, no Blind Person’s Allowance, and no Marriage Allowance involved at all. It’s easy to assume the £12,570 figure is “your allowance” doing double duty for both taxes; it isn’t — it’s two unrelated thresholds that happen to share a number this year.
Class 4 is also the same everywhere in the UK — unlike Income Tax, National Insurance isn’t devolved, so a Scottish sole trader pays Class 4 at the identical 6%/2% rates as everyone else, even though their Income Tax runs through a different band table.
Trading Allowance vs. Actual Expenses
You can shelter up to £1,000 of trading income with the trading allowance, claiming nothing else — no receipts, no records. Or you can deduct your actual business expenses instead. You can’t do both in the same year. If your real expenses are under £1,000, the flat allowance wins with zero paperwork; once they pass £1,000, deducting the real figure wins. This calculator runs both numbers and uses whichever gives you the lower (better) trading profit automatically, and tells you which one it picked.
One consequence worth knowing: if your total trading income is £1,000 or less for the year, the trading allowance wipes it out completely — in most cases you don’t even need to declare it to HMRC.
Class 2 National Insurance — Usually Free Now
Since the 2024/25 reform, most self-employed people never actually pay Class 2 National Insurance any more. Once your trading profit reaches the £7,105 Small Profits Threshold, you’re automatically treated as having paid it — your State Pension and contributory-benefit record is protected at no cost. Below that threshold, nothing is charged, but you can choose to pay it voluntarily (£3.65/week, £189.80/year) if you want that year to count toward your NI record — a decision about pension years, not really a tax question.
How We Calculate Your Bill
- Start with your gross trading income.
- Subtract either your actual expenses or the £1,000 trading allowance — whichever leaves you with the lower trading profit.
- Run that trading profit through the Income Tax engine: Personal Allowance (tapered above £100,000), plus Blind Person’s/Marriage Allowance if applicable, then the rUK or Scottish bands.
- Separately, run the same trading profit through Class 4 National Insurance: 6% between £12,570–£50,270, 2% above.
- Check Class 2: free above £7,105 profit, optional below it.
- Add Income Tax + Class 4 for your Self Assessment bill. If that’s £1,000 or more, project two payments on account of half that amount each, assuming next year looks like this one.
Worked Example
A sole trader in England with £40,000 gross trading income and no expenses to claim: the £1,000 trading allowance beats claiming nothing, leaving £39,000 profit. Income Tax on that (after the £12,570 Personal Allowance) is £5,486.00. Class 4 National Insurance is 6% of the £26,430 between £12,570 and £39,000, which is £1,585.80. Total Self Assessment bill: £7,071.80. Since that’s over £1,000, expect two payments on account of £3,535.90 each next 31 January and 31 July, on top of whatever you owe when you actually file.
Payments on Account, Explained
The part that catches new sole traders out: HMRC doesn’t just want this year’s tax — if your Income Tax plus Class 4 bill is £1,000 or more, you also pre-pay half of it again toward next year, split across two dates (31 January and 31 July). A first-time filer can therefore owe 150% of their actual tax bill in one go the first January: the full amount for the year just finished, plus 50% again as an advance. It evens out in later years since each payment is a fixed 50%, adjusted at the following January once your real bill is known — but it’s a genuine cash-flow shock worth planning for, which is exactly why this calculator projects it rather than only showing “what you owe this year.”
Who Should Use This Calculator?
Sole traders who want a realistic Self Assessment estimate before they file — checking a quarter’s earnings, setting aside the right amount each month, or understanding why the payment due in January is bigger than expected. It’s built for self-employment trading profit specifically: no separate PAYE job, savings interest, dividends, property income or capital gains, and no relief-at-source pension contributions (a different, band-extending calculation this tool doesn’t attempt).
What This Calculator Doesn’t Cover
If you also have a salaried job, use the separate UK Income Tax Calculator for that income and add the two results together — this tool assumes self-employment is your only income. It also doesn’t model Married Couple’s Allowance, student loan repayments, or relief-at-source pension contributions.
Important Tax-Year Information
Tax year: 2026/27 (6 April 2026 to 5 April 2027). Last verified against official sources: 2026-09-08. This calculator will be updated whenever HMRC changes any figure it uses — Class 4/Class 2 thresholds and the trading allowance are reviewed independently of the Income Tax Personal Allowance, so watch for them to move on their own schedule.
Official Sources
- GOV.UK — Self-employed National Insurance rates
- GOV.UK — Tax-free allowances on trading income
- GOV.UK — Understand your Self Assessment tax bill: Payments on account
- GOV.UK — Income Tax rates and Personal Allowances
- GOV.UK — Income Tax in Scotland
Frequently Asked Questions
What tax do I pay on self-employment profit?
Income Tax (0/20/40/45% rUK, or the six Scottish bands) plus Class 4 National Insurance (6% then 2%). Class 2 is now free above £7,105 profit.
Should I claim the trading allowance or my actual expenses?
Whichever is larger — the £1,000 allowance needs no records, actual expenses win once they exceed £1,000. You can’t claim both; this calculator picks automatically.
Do I still pay Class 2 National Insurance?
Almost never as an actual payment — above £7,105 profit you’re treated as having paid it for free. Below that, £3.65/week is optional.
What are payments on account?
If your Income Tax plus Class 4 bill is £1,000+, you pay half again in advance toward next year, by 31 January and 31 July, settled the following January once your real bill is known.
Does this include tax on a separate PAYE job?
No — self-employment trading profit only. Add the UK Income Tax Calculator’s result for any salaried income separately.
This calculator provides an estimate based on the tax rules and assumptions stated above. It models self-employment trading profit only — not a combined PAYE job, savings interest, dividends, property income, capital gains, or relief-at-source pension contributions — and its payments-on-account projection assumes next year’s profit matches this year’s. Your actual liability may differ. Check GOV.UK or a qualified accountant for advice about your specific situation.
