https://www.britannica.com/topic/income-tax#ref592192
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This is a form of income splitting in which the single graduated rate schedule is applied to a figure arrived at by dividing total family income by the number of “units” represented, with each child counting as half a unit. The tax, as so determined on a fraction of the family’s income, is then multiplied by the number of family “units” to arrive at the family’s tax liability.

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France is the only country to practice a family quotient system. Each family is assigned a number of tax parts or shares, P, based on its composition; the shares correspond roughly to the family’s number of consumption units (CU), as these are defined by the OECD and INSEE; the tax system assumes that each family member has a standard of living equivalent to that of a single earner with revenue R/P; the family is then taxed like P single earners with income R/P.

The degree of redistribution assured by the tax system is determined by the tax schedule, which defines the progressivity of the tax system; it is the same for all categories of households.

The family quotient (QF) is thus a logical and necessary component of a progressive tax system. It does not provide any specific support or benefit to families; it merely guarantees a fair distribution of the tax burden among families of different sizes but with an equivalent standard of living. The QF does not constitute an arbitrary support to families, which would increase with income, and which would obviously be unjustifiable.

https://www.ofce.sciences-po.fr/blog/in-defense-of-frances-f...

quotient: A degree or amount of a specified quality or characteristic

https://en.oxforddictionaries.com/definition/quotient

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