How income tax works

Income tax feels complicated because it is described badly, not because it is hard. The underlying idea takes one paragraph.

The core idea

Your income is sliced. Each slice has a rate. You add up the tax on each slice. That is it.

In a progressive system, the first slice is usually tax-free (the personal allowance), the next slice is taxed at a basic rate, and later slices at higher rates. Crucially, moving into a higher band only affects the income above that threshold - never everything you earn.

A worked example

Suppose a system with a 12,000 tax-free allowance, 20% on the next 38,000, and 40% above that. Someone earning 60,000:

• First 12,000 - no tax
• Next 38,000 - taxed at 20% = 7,600
• Remaining 10,000 - taxed at 40% = 4,000
• Total income tax = 11,600

Their top rate is 40%, but 11,600 on 60,000 is an effective rate of about 19.3%. That distinction matters. When people say "I do not want a rise, it will push me into the higher band", they are picturing the whole salary being re-taxed. It is not.

What counts as income

Employment income is the obvious one, but income tax typically also reaches self-employment profit, rental income, pension income, and often savings interest and dividends (usually with their own allowances and rates). Some income is exempt or taxed separately - capital gains, for instance, generally has its own regime.

What comes off before tax

Certain things reduce the income tax is calculated on. Workplace pension contributions are the most common and the most valuable - a contribution made from pre-tax pay effectively costs you less than its face value, because you would have paid tax on that money anyway. Charitable giving schemes and some benefits work similarly.

This is why two people on identical gross salaries can pay noticeably different tax.

How it gets collected

If you are employed, tax is usually withheld at source - deducted before you are paid. You never see the money, which is convenient but also means errors are easy to miss. If you are self-employed, you generally calculate and pay it yourself, which is why setting money aside as you earn matters so much (Track H).

Countries differ, structure does not

Rates, bands, allowances and names change dramatically between countries. The mechanism - allowance, slices, rates, collection - is remarkably consistent. Learn the structure once and you can read any country's system.

Put your salary into the mySal calculator to see your own slices, in your own country, with real numbers.