Tax and NI
Self Assessment tax calculator
HMRC’s own calculation stacks every kind of income in a fixed order, then subtracts what was taxed at source; this tool follows the same order.
With £26,000 of wages and £14,000 of self-employed profit in 2026/27, the Self Assessment bill in England, Wales or Northern Ireland is £2,886: £2,800 of Income Tax not already taken through PAYE and £86 of Class 4. The total Income Tax on all £40,000 of income is £5,486, but the employer has already deducted about £2,686, so only the difference goes on the return. HMRC builds the figure in a set order: non-savings income such as wages and profit first, then savings, then dividends on top; the Personal Allowance of £12,570 is used once, against the first income in that order. Class 4 is charged on the profit alone, so wages never raise it. Student loan repayments are added on income above your plan threshold. Because this bill passes £1,000, a first payment on account of £1,443 is added on 31 January 2028.
Self Assessment bill 2026/27
£2,886
Put aside 20.6 % of your profit · next £100 of profit costs 26.0 %
| Profit | £14,000 |
| Income Tax not taken by PAYE | £2,800 |
| Class 4 National Insurance | £86 |
| Class 2 | treated as paid |
| Kept from your profit | £11,114 |
When you pay, if 2026/27 is your first year
| 31 January 2028: bill + first payment on account | £4,329 |
| 31 July 2028: second payment on account | £1,443 |
Each payment on account is half of £2,886 (Income Tax and Class 4, loans excluded). How payments on account work
Making Tax Digital at this turnover
Turnover of £16,000 is under every threshold announced so far (the lowest is £20,000). Check your start date
Figures checked by Radif Partners · Editorial policy · How we calculate
The calculation, line by line
When you submit a return, HMRC produces a tax calculation, often called an SA302 because of the old form number. It reads like the table below, which reproduces the default case of the calculator: a part-time employee earning £26,000 who also runs a small business with £16,000 of takings and £2,000 of costs.
| Line | Amount |
|---|---|
| Wages (P60) | £26,000 |
| Self-employed profit | £14,000 |
| Total income | £40,000 |
| Personal Allowance | −£12,570 |
| Income Tax on all income | £5,486 |
| Less tax deducted through PAYE | −£2,686 |
| Class 4 on the profit | £86 |
| Balance for the year | £2,886 |
| First payment on account | £1,443 |
| Due on 31 January | £4,329 |
The PAYE figure here is an estimate of what a standard tax code takes from £26,000 over a full year. On your real return you copy the tax shown on your P60 instead, and any difference flows straight into the balance. If your employer used an emergency code, or you changed jobs mid-year, the real figure can be noticeably higher or lower.
The order HMRC applies
Income Tax rules sort income into layers. Non-savings income, which covers wages, trading profit, pensions and rent, sits at the bottom. Savings interest comes next and dividends go on top. The Personal Allowance is used against the lowest layer first, and each layer fills the bands from where the previous one stopped (GOV.UK, Income Tax rates). This is why a dividend can be taxed at the upper dividend rate even when the salary alone was comfortably basic rate: by the time dividends are counted, the basic band may already be full.
Dividends have their own rates, 10.75 %, 35.75 % and 39.35 %, and a £500 allowance that is taxed at nothing but still takes up band space (GOV.UK, tax on dividends). A sole trader with shares in a former employer, or someone who also owns part of a small company, should put those dividends in the calculator, because they change the band that the profit pushes into.
What is not on the bill
Employee National Insurance on wages is settled through payroll and never appears on the return. Class 2 is no longer charged; with profit of £7,105 or more it is treated as paid. Class 4 is charged on profit alone, at 6 % above £12,570 and 2 % above £50,270 (GOV.UK, self-employed National Insurance), so an employee earning £45,000 with £20,000 of side profit still pays the full 6 % on the profit: £446 here, while the Income Tax due through the return is £6,946, most of it at the higher rate.
From the calculation to the payment
The balance and the first payment on account are both due on 31 January 2028 for 2026/27, and the second payment on account on 31 July 2028 (GOV.UK, payments on account). No payments on account are set when the bill is under £1,000, or when more than 80 % of your tax was already deducted at source, which is common for employees with a modest side income. The return itself must be filed online by the same January date, or on paper by 31 October 2027 (GOV.UK, deadlines).
If PAYE took more than the tax due on all your income, for example because a tax code over-collected or the business made no profit, the calculation ends in a repayment. Enter the profit as nil in the calculator to see the tax on wages alone; the tax return guide covers claiming the money back.
For the practical side of running a business next to a job (registration, the tax code and the trading allowance), see the job plus self-employment page.