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Administration

Income tax is generally collected in one of two ways: through withholding of tax at source and/or through payments directly by taxpayers. Nearly all jurisdictions require those paying employees or nonresidents to withhold income tax from such payments. The amount to be withheld is a fixed percentage where the tax itself is at a fixed rate. Alternatively, the amount to be withheld may be determined by the tax administration of the country or by the payer using formulas provided by the tax administration. Payees are generally required to provide to the payer or the government the information needed to make the determinations. Withholding for employees is often referred to as "pay as you earn" (PAYE) or "pay as you go."

Income taxes of workers are often collected by employers under a withholding or pay-as-you-earn tax system. Such collections are not necessarily final amounts of tax, as the worker may be required to aggregate wage income with other income and/or deductions to determine actual tax. Calculation of the tax to be withheld may be done by the government or by employers based on withholding allowances or formulas.

Nearly all systems require those whose proper tax is not fully settled through withholding to self-assess tax and make payments prior to or with final determination of the tax. Self-assessment means the taxpayer must make a computation of tax and submit it to the government. Some countries provide a pre-computed estimate to taxpayers, which the taxpayer can correct as necessary.

The proportion of people who pay their income taxes in full, on time, and voluntarily (that is, without being fined or ordered to pay more by the government) is called the voluntary compliance rate. The voluntary compliance rate is higher in the US than in countries like Germany or Italy. In countries with a sizeable black market, the voluntary compliance rate is very low and may be impossible to properly calculate.