Income Tax: How Earnings Are Reduced by Tax Systems

Income tax is a mandatory payment applied to income earned by individuals.

In practice, this means that part of what a person earns is transferred to the public system before they receive net income.

Understanding income tax is essential for explaining why gross income and net income differ.

What is income tax

Income tax is a compulsory levy imposed on income by law.

• established by tax legislation
• assessed on taxable income
• used to finance public expenditure

The exact amount depends on system rules, rates, and allowances.

Income tax in employment

• calculated on wages or salaries
• withheld by the employer
• transferred to public authorities

In practice, this means that employees usually do not receive the full gross amount, as tax is deducted during payroll processing.

Income tax structures

• progressive tax systems
• flat tax systems
• tax‑free thresholds

These structures determine how tax increases with income.

Why income tax exists

Income tax is one of the primary ways governments finance public expenditure.

• supports public services
• helps finance public administration
• provides revenue for infrastructure and government programmes

In practice, income tax connects individual earnings with the financing of services and institutions used across society.

For a comparison between income tax and social contributions, see Why Both Reduce Your Salary.

A practical example

An employee may agree to a gross salary with an employer, but the full amount is not usually received as take-home pay.

Before payment is made, income tax is deducted according to the rules of the tax system.

• gross salary represents income before tax
• income tax reduces the amount available to the worker
• the remaining amount contributes to net income

In practice, income tax is one of the main reasons why gross income and net income are different.

For a step-by-step explanation of how deductions affect salary, see How Gross Pay Becomes Take‑Home Income.

Income tax in comparisons

• compare tax burdens
• explain net income differences
• analyse system design

In practice, this means that differences in tax systems are a major factor behind variations in take-home pay across countries.

Scope limitations

• tax rates or brackets
• allowances or credits
• household taxation rules
• filing procedures
• tax optimisation

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