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State Income Tax vs. Federal Income Tax: An Overview

The United States has a multi-tiered income tax system under which taxes are imposed by federal, state, and sometimes local governments. Federal and state income taxes are similar in that they apply a tax rate to taxable incomes, but they can differ considerably with respect to those tax rates and how they're applied, as well as to the types of incomes that are taxable, and the deductions and tax credits that are allowed.

State Income Taxes

State income tax rates can vary considerably from state to state. In fact, Alaska, Florida, Nevada, South Dakota, Texas, Washington, and Wyoming have no income tax at all. New Hampshire and Tennessee tax only interest income and dividends, not earned income from salary and wages, and Tennessee is in the process of repealing even this taxation by 2022.

All other states have either flat or progressive income tax systems. A flat system is a single rate that applies to all levels of income. Eight states use this system as of 2019: North Carolina (5.499%), Massachusetts (5.10%), Utah (5%), Colorado (4.63%), Michigan (4.25%) Illinois (3.75%), Indiana (3.23%), and Pennsylvania (3.07%).

Thirty-three states tax according to marginal, progressive systems where higher levels of income are taxed at a greater percentage, a commonality shared with the federal income tax system. Each "bracket" of income is taxed at a higher percentage. Some states base their brackets on the federal tax code, but many states implement their own. Some adjust their brackets annually to keep pace with inflation, but others do not.

Hawaii has 12 tax brackets as of 2019, while Kansas only imposes two. California's progressive tax system has the highest top tax rate of 13.3% on incomes above $1 million, followed by Hawaii at 11%. North Dakota (2.9%) and Arizona (4.54%) are among the states with the lowest top tax rates.

Federal Income Tax

The Internal Revenue Code (IRC) governs federal income tax in the U.S., and the IRC underwent some significant changes in 2018 with the passage of the Tax Cuts and Jobs Act (TCJA). But the U.S. continues to implement a progressive tax system. There are seven tax seven brackets and marginal tax rates at the federal level: 10%, 12%, 22%, 24%, 32%, 35%, and 37%. The top rate of 37% is significantly more than California's 13.3%, and it kicks in at only $510,300 in taxable income, whereas California's high rate doesn't apply until a taxpayer has more than $1 million in taxable income.