How to use
- Enter your turnover: everything you were paid for your work in the 2026/27 tax year (6 April 2026 to 5 April 2027).
- Enter your allowable expenses, or switch to the £1,000 trading allowance if your costs are small.
- If you also have a job, add your salary before tax. It is optional.
- Choose Scotland if you are a Scottish taxpayer.
You get the total Income Tax and Class 4 National Insurance on your profit, what you keep after tax, how much to put aside each month and whether you need to make payments on account.
How it is calculated
Profit = turnover − allowable expenses (or − £1,000 trading allowance)
Income Tax (England, Wales and Northern Ireland, 2026/27):
| Band | Taxable income | Rate |
|---|---|---|
| Personal Allowance | Up to £12,570 | 0% |
| Basic rate | £12,571 to £50,270 | 20% |
| Higher rate | £50,271 to £125,140 | 40% |
| Additional rate | Over £125,140 | 45% |
The Personal Allowance goes down by £1 for every £2 of income above £100,000, so it is zero from £125,140.
Scottish Income Tax (2026/27): starter 19% (£12,571 to £16,537), basic 20% (to £29,526), intermediate 21% (to £43,662), higher 42% (to £75,000), advanced 45% (to £125,140) and top 48% above that.
Class 4 National Insurance: 6% of profit between £12,570 and £50,270, plus 2% of profit above £50,270.
If you have a salary, the calculator works out tax on salary plus profit, then takes off the tax on the salary alone (already paid through PAYE). What is left is the tax your business profit adds.
Examples
Profit only, no other income, 2026/27:
| Profit | Income Tax | Class 4 NI | Total | Set aside a month |
|---|---|---|---|---|
| £15,000 | £486 | £145.80 | £631.80 | £52.65 |
| £30,000 | £3,486 | £1,045.80 | £4,531.80 | £377.65 |
| £50,000 | £7,486 | £2,245.80 | £9,731.80 | £810.98 |
| £70,000 | £15,432 | £2,656.60 | £18,088.60 | £1,507.38 |
The same profits in Scotland: £607.50, £4,496.87, £11,227.85 and £20,038.65.
Job plus side business: a £35,000 salary and £15,000 profit from a side business (£20,000 turnover, £5,000 expenses). The profit is all taxed at 20% (£3,000) and Class 4 NI on it is £145.80, so the Self Assessment bill is £3,145.80.
Payments on account
If your Self Assessment bill is £1,000 or more, and less than 80% of your total tax was taken at source (for example through PAYE), HMRC asks for advance payments towards next year’s bill:
- 31 January: the balance for the year just ended plus the first payment on account (half of that year’s bill)
- 31 July: the second payment on account
For a first year with a 2026/27 bill of £4,531.80, that is £6,797.70 by 31/01/2028 and £2,265.90 by 31/07/2028. If next year’s profit will be lower, you can ask HMRC to reduce your payments on account.
What is not included
Student loan repayments, pension contributions and Gift Aid (which extend your basic rate band), Class 1 NI on a salary, losses carried forward, and the Marriage Allowance. The figures are an estimate: your Self Assessment calculation from HMRC is the final word.