Marginal vs effective tax: why a raise never costs you money

The most persistent myth in personal finance is that crossing into a higher tax bracket can leave you worse off. In a progressive system it cannot, and the reason is that brackets tax slices of income, not the whole of it.

Suppose the bands are 0% up to 300,000, 5% to 600,000, 10% to 800,000 and 15% above. Earning 800,001 does not tax you at 15% on 800,001. It taxes one unit at 15%. Your total tax rises by fifteen paise. Everything below the threshold keeps its old, lower treatment.

This gives you two rates, and it is worth knowing both. On 900,000 of taxable income under those bands the total tax is 50,000. The effective rate — what you actually paid across everything — is 5.6%. The marginal rate, which governs your next raise and the value of any deduction, is 15%.

The distinction matters practically. Use the marginal rate to price decisions at the edge: how much a bonus nets, how much a retirement contribution saves, whether overtime is worth the evening. Use the effective rate to budget, because that is the number that actually leaves your account across the year.

One real exception exists, and it is not a tax phenomenon. Some benefits and subsidies have hard eligibility cliffs, so earning one unit more can withdraw a payment worth far more than the tax on it. That is a means-testing design flaw, not bracket creep, and it is worth checking if you are near such a threshold.

The practical takeaway: never turn down income because of brackets, and never estimate your tax by multiplying your salary by your top rate. Run the bands, then judge.