Flat Tax
A tax system with a single rate applied to all income levels. Several US states use flat income tax rates, including Illinois (4.95%), Colorado (4.4%), and Pennsylvania (3.07%).
A flat tax applies the same rate to all taxable income, regardless of how much you earn. Unlike progressive systems with multiple brackets, a flat tax has just one rate. Several US states use flat income taxes, including Illinois (4.95%), Colorado (4.4%), Pennsylvania (3.07%), Indiana (3.0% for 2025, phasing down to 2.95% in 2026), Michigan (4.25%), and Utah (4.5% for 2025, 4.45% for 2026).
Supporters of flat taxes argue they are simpler, more transparent, and create fewer distortions in economic behavior. Since the rate does not change with income, there is no incentive to defer or shift income across brackets. Administration is also simpler with one rate to apply.
In practice, even flat-tax states maintain some progressivity through personal exemptions and standard deductions that effectively exempt lower-income earners from tax entirely. A single person earning $20,000 may pay an effective rate well below the flat rate after exemptions, while someone earning $500,000 pays close to the full rate. Several states have recently converted from progressive to flat tax systems, including Arizona, Iowa, and Georgia.
How it works
A flat tax applies one single rate to all taxable income, regardless of how much a person earns, in contrast to a progressive system with multiple brackets. Several US states use this structure, including Illinois at 4.95%, Colorado at 4.4%, and Pennsylvania at 3.07%, and other states have converted from progressive to flat systems in recent years.
You meet a flat tax on your state return in the states that use one — there is no bracket table to navigate, since the same percentage applies whether your taxable income is $20,000 or $500,000. This makes flat-tax state returns considerably simpler to calculate than progressive ones, with no need to determine which slice of income falls into which bracket.
A flat rate does not necessarily mean the system has zero progressivity in practice — most flat-tax states still apply personal exemptions or a standard deduction before the flat rate kicks in, which shields a chunk of income from tax entirely and means lower earners can end up with an effective rate well below the stated flat rate, while very high earners pay close to the full rate on nearly all their income. Some states, like Indiana and Utah, have also been phasing their flat rate downward gradually year by year rather than cutting it all at once.
Example: exemptions still create some progressivity
A flat-tax state applies a 4.5% rate to all taxable income, but exempts the first $12,000 of income through a standard deduction. One taxpayer earns $20,000 and another earns $500,000.
The first taxpayer pays 4.5% only on $8,000 of taxable income after the exemption, an effective rate well under 2% of their total $20,000 earned. The second taxpayer's $12,000 exemption barely matters against $500,000 of income, so their effective rate lands very close to the full 4.5% flat rate.
Frequently asked questions
Is a flat tax the same rate no matter how much I earn?
Which US states use a flat income tax?
Is a flat tax simpler to calculate than a progressive tax?
Related Terms
Progressive Tax
A tax system where rates increase as income rises, with higher earners paying a larger percentage. The US federal income tax and most state income taxes use progressive brackets.
State Income Tax
Income tax levied by individual states, in addition to federal income tax. Rates and structures vary widely — some states have no income tax, while others have rates up to 13.3%.
Effective Tax Rate
Your total federal income tax divided by your total income, expressed as a percentage. It represents the average rate at which your income is actually taxed.