How income tax is actually calculated
Income tax in most countries is progressive: income is divided into bands, and each band is taxed at its own rate. A higher rate applies only to the income above the threshold where that band begins, never to the whole amount. This is the most misunderstood part of the system — a raise that pushes you into a higher band cannot leave you with less money than you had before it.
Two different mechanisms reduce what you owe, and they are not interchangeable. A deduction lowers the income being taxed, so its value depends on your marginal band — the same deduction is worth more to a higher earner than a lower one. A rebate lowers the calculated tax itself, one unit for one unit, no matter which band you sit in.
Where a jurisdiction offers more than one regime — typically a higher-rate structure that permits deductions alongside a lower-rate structure that does not — neither wins universally. The answer depends entirely on how much you can genuinely claim. Compute the final tax under each and compare the totals; comparing headline rates alone tells you nothing useful.
Worked example
The bands below are invented purely to demonstrate the arithmetic. They are not the rates of any country and must not be used for a real calculation — confirm current bands and thresholds with your own tax authority. Assume an illustrative structure of 0% on the first 3,00,000, 10% on the next 3,00,000, 20% on the next 4,00,000 and 30% on everything above 10,00,000, applied to an income of 12,00,000.
| Input | Value |
|---|
| Total income | 12,00,000 |
| Band 1 — 0% on 3,00,000 | 0 |
| Band 2 — 10% on 3,00,000 | 30,000 |
| Band 3 — 20% on 4,00,000 | 80,000 |
| Band 4 — 30% on 2,00,000 | 60,000 |
| Total tax | 1,70,000 |
| Marginal rate | 30% |
| Effective rate | 14.17% |
The marginal rate is 30% but the effective rate is 14.17%, because most of the income was taxed at lower rates or not at all. Now claim a deduction of 1,00,000: taxable income falls to 11,00,000 and the tax to 1,40,000 — a saving of 30,000, which is exactly the deduction multiplied by the marginal rate. A rebate of 1,00,000 would instead cut the tax straight to 70,000. Same headline figure, very different effect. All of this comes from the illustrative bands above, not from any real schedule.
How to use this calculator
- Enter your total income from every source, not just salary — interest, rent and capital gains usually count too.
- Enter each deduction separately, and only where you can actually produce evidence for the claim.
- Run the calculation under every regime available to you and compare the final tax amounts, not the headline rates.
- Read the effective rate alongside the total — it tells you what share of your income the tax actually consumed.
- Confirm current bands, thresholds and eligibility with an official source before filing; these change frequently.
Frequently asked questions
Does moving into a higher tax band reduce my take-home pay?
No. Only the income above the new threshold is taxed at the higher rate — everything below it continues to be taxed exactly as before. Earning more always leaves you with more after tax in a purely progressive system. The fear of a raise costing money comes from misreading the band as applying to the whole income.
What is the difference between a deduction and a rebate?
A deduction is subtracted from income before tax is computed, so it saves you the deduction multiplied by your marginal rate. A rebate is subtracted from the tax itself, so it saves its full face value. A rebate is therefore worth more than a deduction of the same size, for everyone.
Why is my effective rate lower than my tax band?
Because your top band only applies to the last slice of your income. The earlier slices were taxed at lower rates, and some were probably not taxed at all. The effective rate averages across all of them, so in a progressive system it sits below the marginal rate by definition.
How do I choose between two tax regimes?
Compute the final tax under both using your actual, documented deductions — not the ones you intend to make. A regime with lower rates and no deductions often wins for someone claiming little, and loses for someone with substantial housing interest, retirement contributions or insurance premiums to offset.
Is the tax withheld from my salary the final amount I owe?
Usually not exactly. Withholding is an estimate based on what your employer knows, which excludes income from other sources and deductions you declared late or not at all. Your return reconciles the estimate against the real liability, producing either a refund or a balance due.
Do the rates in the example above apply to me?
No. They are invented to illustrate how banding works and correspond to no jurisdiction. Real bands, thresholds, rebates and deduction limits are revised regularly and differ by country, residency status and sometimes age. Always take the current figures from your tax authority rather than from any article.
This calculator is an educational tool. Results are estimates based on the inputs you provide and do not constitute financial advice. Verify figures with your bank, broker or a qualified advisor before acting on them.