Understand How Tax Brackets Work

Someone told you that getting a pay rise would push you into a higher tax bracket and cost you money. That is not how tax brackets work. This explains how they do work, with a calculation that shows exactly how much tax is paid on each portion of a given salary, plus the personal allowance, National Insurance, and the one thing everyone gets wrong about tax brackets.

Explain how UK income tax brackets work in plain English. Include:
1. How marginal rates work: why earning more does not mean you take home less, and what 'marginal rate' actually means
2. A worked example using a salary of {EXAMPLE_SALARY}: show exactly how much tax is paid on each portion of the income, with the calculation visible
3. What National Insurance is and how it interacts with income tax on a payslip
4. The personal allowance: what it is, why it phases out above a certain income, and when that matters
5. One common misconception about tax brackets, corrected in one clear paragraph

Assume no prior knowledge. Use round numbers. Show all calculations. Write as if explaining to a confident adult who has never had to file a tax return.