Your salary or turnover is not what you pay tax on. Understanding what HMRC actually counts can save you a meaningful sum every year.
Most people assume they are taxed on everything they earn. They are not. A sole trader with £40,000 of turnover might have a taxable income closer to £26,000 once allowable expenses and the Personal Allowance are stripped away, and that difference determines whether they pay £3,000 or £7,000 in income tax. Getting this figure right is the foundational skill of managing your own tax affairs.
HMRC casts a wide net. Income includes your employment wages, self-employment profits, rental income, pension payments, interest on savings above the Personal Savings Allowance, dividends above the £500 annual dividend allowance, and certain state benefits such as the State Pension and Carer's Allowance. It is not limited to cash payments: benefits in kind, such as a company car, are assessed as income and added to your total.
What does not count is equally important. Statutory Maternity Pay is taxable, but Child Benefit itself is not (though the High Income Child Benefit Charge can claw some back). Redundancy pay up to £30,000 is exempt. Premium Bond prizes, lottery winnings, and income earned inside an ISA are all outside scope entirely. Income from trading or property below the £1,000 trading and property allowances respectively is also exempt.
The calculation flows in a consistent order: start with gross income, subtract allowable deductions, then subtract allowances. What remains is taxable income, and it is that figure against which the tax bands are applied.
| Step | Amount |
|---|---|
| Gross turnover | £40,000 |
| Less allowable business expenses | £8,000 |
| Net self-employment profit | £32,000 |
| Less Personal Allowance (2025/26) | £12,570 |
| Taxable income | £19,430 |
| Basic rate tax at 20% | £3,886 |
Without accounting for expenses and allowances, you might have assumed the bill was 20% of £40,000, which is £8,000. The actual liability is less than half that. You can run these numbers for your own situation using the sole trader tax calculator to see how your specific expenses change the picture.
Once you have your taxable income figure, it is sliced into bands. In England, Wales and Northern Ireland for 2025/26:
| 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 | Above £125,140 | 45% |
Scotland sets its own income tax rates and bands, which differ from the rest of the UK above the Personal Allowance. Scottish taxpayers pay the same National Insurance but different income tax rates, so the term "taxable income" applies equally but the rates applied to it diverge.
Note that the Personal Allowance tapers between £100,000 and £125,140. You lose £1 of allowance for every £2 of adjusted net income above £100,000, which creates an effective 60% marginal tax rate in that range. Understanding your Personal Allowance precisely matters most at that income level.
For someone in PAYE employment, taxable income is calculated largely automatically. Gross salary, minus any pension contributions made through salary sacrifice, minus professional subscriptions claimed via a P87, minus the Personal Allowance. The result is what HMRC instructs your employer to tax you on each month via your tax code.
Sole traders and the self-employed face a more manual process. Their taxable income is built from a profit and loss account, not a payslip. Allowable expenses, capital allowances, and any overlap relief from earlier accounting periods all reduce the profit figure before the Personal Allowance comes off. If you want a quick sense of where you stand as an employee before diving into a full self-assessment, the salary income tax calculator lets you check your effective rate in seconds.
The most common error is conflating turnover with taxable income. A freelancer invoicing £60,000 can easily assume they sit in the higher rate band, when legitimate expenses and pension contributions might pull their taxable income below £50,270 entirely, keeping every pound at 20% rather than 40%.
The second mistake is missing exempt income and reporting it unnecessarily. Including ISA interest or the first £1,000 of a side hustle covered by the trading allowance inflates your declared income and your bill.
The third, and arguably the most expensive, is failing to claim deductions that are genuinely available: use-of-home costs, professional indemnity insurance, subscriptions, mileage at HMRC approved rates, and accountancy fees are all allowable for most self-employed people. Each unclaimed pound of expense is effectively taxed at your marginal rate.
Taxable income is not what you earn. It is what is left after HMRC's rules have finished stripping away everything you are legally allowed to exclude.
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