Taxes · Explainer
Marginal and effective tax rates are not the same number
A higher bracket taxes the next unit of income, not all of it. Confusing the two produces genuinely bad decisions.
The short answer
- Marginal rate applies to the next currency unit earned.
- Effective rate is total tax divided by total income, and is always lower.
- Withdrawn allowances can create marginal rates higher than any headline band.
Progressive income tax systems apply rising rates to successive slices of income. Moving into a higher band therefore raises the tax on the additional income only. A pay rise cannot reduce take-home pay through bracket movement alone.
The two rates
- Marginal rate: the tax paid on one more unit of income. It governs decisions — overtime, bonuses, pension contributions.
- Effective rate: total tax divided by total income. It describes the overall burden and is what belongs in a budget.
Where the exception lives
Cliff edges do exist, but they come from benefit withdrawal and allowance tapering rather than from the bands themselves. Where an allowance is withdrawn as income rises, the effective marginal rate over that band can exceed the top headline rate — which is exactly the range where pension contributions or salary sacrifice are most efficient.
Different income, different treatment
Employment income, dividends, savings interest and capital gains are frequently taxed at different rates with separate allowances. Comparing investments on pre-tax returns while ignoring which pot they sit in is a common and expensive error.
Sources
- Tax brackets and rates — Internal Revenue Service
- Income tax rates and allowances — GOV.UK / HMRC
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