The United States actually spends roughly as much through tax expenditures as it collects in nominal personal income tax revenues.

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In ten recent examples, Flat Tax implementation did not lead to a meaningful decline in revenues in either nominal terms or as a percentage of GDP.

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In fiscal 2001 (which ended on June 30th), state revenues increased by 4.5% in nominal terms.

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Instead, I looked at how much money each would collect in revenues and how much it would spend in 2014 and in 2023, in nominal dollars and as a share of the Gross Domestic Product.

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