Knowing your marginal rate tells you the true cost of earning more, and why a pay rise does not always mean you keep what you expect.
A freelancer who pushes their annual profit from £49,000 to £55,000 might expect to pocket most of that £6,000 extra. In reality, every pound of it is taxed at 40 per cent, not the 20 per cent they paid on most of their income. That gap between expectation and reality is exactly what the marginal tax rate is designed to explain.
The UK uses a progressive tax system. Income does not all get taxed at the same rate. Instead, each slice of earnings is taxed at the rate that applies to that slice, and your marginal rate is simply the rate at which the topmost slice is taxed.
Think of your annual income as a stack of £1 coins. The first £12,570 sits in the Personal Allowance zone and is tax-free. The next pounds are taxed at 20 per cent until you reach £50,270. Beyond that, the rate jumps to 40 per cent. Understanding where in the stack your next pound lands is what the marginal rate tells you. For a fuller picture of how each band operates, the guide to UK income tax bands sets out the full structure.
| Income band | Marginal income tax rate |
|---|---|
| Up to £12,570 (Personal Allowance) | 0% |
| £12,571 to £50,270 | 20% |
| £50,271 to £125,140 | 40% |
| Above £125,140 | 45% |
Scotland uses different bands and rates (the starter rate of 19% and the intermediate rate of 21% mean Scottish taxpayers can have different marginal rates even on relatively modest incomes, so it is worth checking your Scottish equivalent).
This is the confusion that causes the most trouble. Your effective tax rate is the average rate across all your income. Your marginal rate is the rate on your last pound only.
Sarah is a self-employed graphic designer. Her profit for 2025/26 is £60,000.
Total income tax: £11,432
Effective rate: £11,432 divided by £60,000 = roughly 19%
But Sarah's marginal rate is 40 per cent. If a client offers her an extra £2,000 project, she will keep only £1,200 of it after income tax alone (before National Insurance). That single figure, 40 per cent, should shape how she prices her work. You can run the same numbers yourself using the salary and income tax calculator.
The most punishing marginal rate in the UK system is not the 45 per cent additional rate. It is the unofficial 60 per cent band that applies between £100,000 and £125,140, and many higher earners do not see it coming.
At £100,000, HMRC begins withdrawing the Personal Allowance at a rate of £1 for every £2 of income above that threshold. By £125,140 the entire £12,570 allowance is gone. This means every £2 of income in that range loses £1 of tax-free allowance, creating an additional 20 per cent income tax liability on top of the standard 40 per cent. The combined effect is a 60 per cent marginal rate.
A sole trader who earns £105,000 and contributes £5,000 into a pension would reduce their adjusted net income back below £100,000, restoring some of their Personal Allowance and cutting their effective marginal rate sharply. If you are approaching this band, understanding higher rate tax in full is worth your time before the end of the tax year.
Marginal income tax rates are only part of the story. Class 4 National Insurance for sole traders in 2025/26 adds 6 per cent on profits between £12,570 and £50,270 and 2 per cent above that. An employed person pays Class 1 at 8 per cent and 2 per cent in the same bands.
For a basic rate taxpayer, the combined marginal rate is 20% income tax plus 6% Class 4 NI, giving an effective marginal deduction of around 26 per cent on each extra pound of self-employed profit below £50,270. At higher rate, it becomes 40% plus 2%, so 42 per cent. These figures matter when a sole trader is deciding whether to incorporate, how to price a contract, or whether a new stream of work is genuinely profitable after tax.
Knowing your marginal rate is not just an academic exercise. It directly affects practical choices:
Pension contributions: A higher rate taxpayer gets 40 per cent relief on contributions, making pensions significantly more valuable than they appear to a basic rate payer.
Dividend planning (for limited company owners): Taking income above the basic rate band triggers higher dividend tax rates; understanding the marginal rate prevents an unpleasant surprise on the Self Assessment return.
Quoting a day rate: A sole trader who wants to take home an extra £500 a month and is in the 40 per cent band needs to earn roughly £840 before tax to achieve it, more once NI is included.
Your marginal rate is the lens through which every extra pound of income should be viewed; confuse it with your average rate and you will consistently mis-price your work or your time.
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