UK self-employed tax calculator — a Self Assessment estimate that shows its working
How much tax will I pay as a self-employed sole trader?
On the worked example on this page — £52,000.00 of income and £14,195.00 of allowable costs including the mileage and working-from-home flat rates — the estimated Self Assessment bill for 2026–27 is £6,561.10: £5,047.00 income tax plus £1,514.10 Class 4 National Insurance. The first 31 January after that year would ask for £9,841.65, because the balance and half of next year's estimated bill are due on the same day.
Sole traders · England, Wales & Northern Ireland or Scotland · tax years 2025–26 and 2026–27 · runs in your browser, nothing you type is stored or sent
Most estimators ask for a profit figure and multiply it. This one starts where your records start — income, costs, business miles, hours working from home — decides for you whether the trading allowance or your actual costs leaves less tax, tapers your Personal Allowance if profit is high, works the bands of your own nation, adds both classes of National Insurance, and then shows the part most people meet as a surprise: payments on account.
Your year
Everything your trade was paid in the year, before any costs (cash basis). Goods, services, phone, insurance and other allowable running costs — WITHOUT vehicle miles or home working hours; those two are added below at HMRC's flat rates.
Simplified expenses: the year's rate per mile is applied automatically — a higher rate up to the mileage threshold, a lower one after it. The rate is a per-year figure and it changed for 2026–27; the result line shows the amount it produced. HMRC's flat rate for working from home, applied month by month. Months under the minimum hours count as zero at the flat rate. Phone and internet are not covered by it — put their business share in costs above.
What you already paid towards this year last January and July, if anything. Used only for the schedule at the bottom. If most of your tax is already deducted before it reaches you, HMRC does not ask for payments on account.
Your estimate
Estimated Self Assessment bill for 2026–27: £6,561.10 — income tax £5,047.00 plus Class 4 National Insurance £1,514.10.
Your actual costs (£14,195.00) beat the £1,000.00 trading allowance — the estimate deducts the costs.
Where the bill comes from
| Line | Amount | Rate | Tax |
|---|---|---|---|
| Personal Allowance | £12,570.00 | tax-free | — |
| Basic rate | £25,235.00 | 20% | £5,047.00 |
| Class 4 National Insurance | £25,235.00 | 6% | £1,514.10 |
| Total | — | — | £6,561.10 |
Class 2 National Insurance: treated as paid — your profit is at or above the small profits threshold, so the year protects your State Pension record without a payment.
When the money is actually due
- 31 January 2028 — balance for the year (£6,561.10) plus the first payment on account for the next one (£3,280.55)
- 31 July 2028 — second payment on account — £3,280.55
- First year with payments on account: the January payment is one and a half bills in a single day. This is the payment that catches people.
What the estimate actually does
- Adds HMRC's flat rates for business miles and home working to the costs you typed, then compares that total against the trading allowance and keeps whichever leaves you less taxable profit — they can never be combined.
- Tapers the Personal Allowance when profit crosses the taper threshold — one pound of allowance lost for every two above it, down to nothing — and only then works the income tax bands of the nation you picked. Scotland has its own bands and rates for trading profit; National Insurance stays UK-wide.
- Adds Class 4 National Insurance between its own profit limits at the year's two rates, and reports Class 2 the way HMRC now treats it: as paid, once profit reaches the small profits threshold — or as a voluntary amount if it does not.
- Builds the payment schedule: the balancing payment, then payments on account at half the bill each — unless the bill is small or most of your tax is collected at source, in which case it says so instead of inventing instalments.
- It is an estimate, not your SA302: HMRC rounds a few figures in your favour when it calculates; this page does not, so the official figure can differ by a few pounds.
- Trading profit only — no employment income alongside, no dividends, no savings interest, no rental income, no CIS deductions, no VAT.
- No loss relief: a loss year shows zero tax here, and carrying the loss elsewhere is not modelled.
- No pension contributions, Gift Aid, Marriage Allowance, student loan repayments or the High Income Child Benefit Charge.
- The mileage flat rate has conditions the form cannot check: it is per vehicle, and once you use the flat rate for a vehicle you keep using it for that vehicle; it is not available if you have already claimed the vehicle's actual costs or capital allowances.
- Scotland's own bands apply to trading profit, which is exactly what this page computes; savings and dividend income would use UK-wide rates, and neither is carried here.
Every rate, limit and rule above is read from the GOV.UK and gov.scot pages listed under Sources, with the capture date shown — none of it is typed from memory.
Making Tax Digital and spreadsheets
Quarterly digital reporting is being phased in for sole traders above an income threshold. HMRC's own guidance on software choices says:
«if you use spreadsheets to record income and expenses, bridging software can connect to them and make your submissions to HMRC» — GOV.UK
This is arithmetic, not tax advice. Rates and thresholds are the captured ones shown under Sources; check anything that decides real money against the linked GOV.UK pages before you act on it.
This page answers one year — the spreadsheet keeps the whole year's books
The same verified arithmetic, carried through a year you actually live: income and expense logs mapped to the self-employment form's own boxes, mileage and home-working flat rates computed as you go, both tax years side by side, and the Self Assessment figures ready when January comes.
See the spreadsheet — $12Questions people actually ask
Is this the same figure HMRC will show me?
Close but not identical by design. HMRC's calculation rounds certain amounts in your favour and handles dozens of income types this page deliberately leaves out. What you get here is the sole-trader mechanics — election, taper, bands, both NIC classes, payments on account — computed exactly and verified against an independent model before the page shipped.
Which mileage rate does it use? I heard the rate changed.
It changed with the 2026–27 tax year, which started on 6 April 2026: the flat rate for the first 10,000 miles in a car or van rose from £0.45 to £0.55 per mile, and the calculator applies whichever belongs to the year you picked. Guides and templates written earlier often still carry the old rate for the new year — worth checking anything you paid for.
Does it work for Scotland?
Yes, as a first-class option, not a footnote. Trading profit in Scotland is taxed on Scotland's own bands and rates, which differ from the rest of the UK at both ends of the scale — while National Insurance is the same UK-wide. Pick Scotland and the band table rebuilds itself; the two nations' figures are independently checked against the same model.
Can I still do my books in a spreadsheet under Making Tax Digital?
HMRC's guidance on choosing software addresses spreadsheets directly — the quotation above is its wording, linked under Sources. The phase-in starts from an income threshold and reaches lower incomes in later years, so when you must join depends on your income, not on how you keep your records.
Why is my January payment so much bigger than my bill?
Payments on account. Once your bill passes the threshold, HMRC asks for next year's tax in advance, in two halves — the first half lands on the same 31 January as the balance for the year just finished. In your first such year that is one and a half bills at once. The schedule at the bottom of the results shows both dates and both amounts for your own figures.
Sources
- Income Tax rates and allowances (HMRC)
- Scottish Income Tax rates and bands (gov.scot)
- Rates and allowances: National Insurance contributions (HMRC)
- Simplified expenses: vehicles (GOV.UK)
- Simplified expenses: working from home (GOV.UK)
- Tax-free allowances on trading income (GOV.UK)
- Payments on account (GOV.UK)
- Making Tax Digital for Income Tax: software (GOV.UK)
