Fourteen states apply a single flat rate to all taxable income in 2026. The rates below are taken directly from each state’s official data file, which was audited against official tax forms and statutes on 2026-10-07.
| State | Flat Rate | Low Confidence? | Starting Point |
|---|---|---|---|
| Arizona (AZ) | 2.50% | Yes* | Federal AGI |
| Indiana (IN) | 2.95% | — | Federal AGI |
| Louisiana (LA) | 3.00% | — | Own (after adjustments) |
| Pennsylvania (PA) | 3.07% | — | Own (gross compensation) |
| Kentucky (KY) | 3.50% | — | Federal AGI |
| Iowa (IA) | 3.80% | — | Federal taxable income |
| North Carolina (NC) | 3.99% | — | Federal taxable income |
| Michigan (MI) | 4.25% | — | Federal AGI |
| Colorado (CO) | 4.40% | — | Federal taxable income |
| Utah (UT) | 4.45% | — | Federal AGI |
| Illinois (IL) | 4.95% | — | Federal AGI |
| Georgia (GA) | 4.99% | — | Federal taxable income |
| Massachusetts (MA) | 5.00% | — | Own |
| Idaho (ID) | 5.30% on income above threshold† | Yes* | Federal taxable income |
* Low confidence means the 2026 official indexed thresholds have not been published by the relevant state agency as of 2026-10-07. The rates themselves are enacted law; the exact income figures at which they apply may shift slightly when indexed amounts are posted.
† Idaho is technically a flat-rate state but with a 0% band first: 0% on the initial $4,811 (single/MFS) or $9,622 (joint/HOH), then 5.3% on income above that threshold. The $4,811 figure is from the 2025 tax year; the 2026 indexed value was not published by the Idaho State Tax Commission as of October 2026. (Idaho STC)
Use the salary comparison calculator to model two states side by side, or the paycheck calculator for your specific gross pay and pay frequency.
How Flat Taxes Work
A flat tax applies one rate to all taxable income above any standard deduction or personal exemption. The taxable base varies by state:
- Federal AGI as starting point: Indiana, Kentucky, Michigan, Illinois, and others begin with your federal adjusted gross income and then apply state-specific deductions or exemptions.
- Federal taxable income as starting point: Iowa, Colorado, North Carolina, and Idaho start after the federal standard deduction, so the first ~$16,100 (single, 2026) is already excluded.
- Gross compensation (“own” basis): Pennsylvania and Massachusetts start from gross wages with no federal standard deduction subtracted. Pennsylvania’s 3.07% on gross wages is therefore effectively higher than its nominal rate implies relative to federal-AGI states.
Worked Example: $60,000 Single Filer
The engine computes the following annual state income tax for a single filer earning $60,000 with no retirement contributions. Federal and FICA taxes are the same across all states and are excluded from this comparison.
| State | Rate | Engine-Computed State Tax |
|---|---|---|
| Arizona (AZ)* | 2.50% | $1,106 |
| Indiana (IN) | 2.95% | $1,741 |
| Louisiana (LA) | 3.00% | $1,415 |
| Pennsylvania (PA) | 3.07% | $1,842 |
| Kentucky (KY) | 3.50% | $1,982 |
| Iowa (IA) | 3.80% | $1,668 |
| North Carolina (NC) | 3.99% | $1,885 |
| Michigan (MI) | 4.25% | $2,299 |
| Colorado (CO) | 4.40% | $1,932 |
| Utah (UT) | 4.45% | $2,247 |
| Illinois (IL) | 4.95% | $2,825 |
| Georgia (GA) | 4.99% | $2,246 |
| Massachusetts (MA) | 5.00% | $2,780 |
* AZ figure is the latest official rate available; low confidence on exact indexed amounts (see above).
The dollar differences reflect both the rate and the taxable base. Louisiana’s lower result at 3.00% versus Indiana’s 2.95% reflects Louisiana’s different deduction structure, not an error. Pennsylvania’s higher dollar amount at 3.07% vs. Iowa at 3.80% reflects that PA starts from gross wages while Iowa starts from federal taxable income (which is already reduced by the ~$16,100 standard deduction). These results are estimates; actual withholding can differ based on exemptions and credits not modeled here.
Comparing Flat-Tax States to Progressive States
A flat rate is predictable. Every additional dollar of income is taxed at the same marginal rate. In a progressive state like California or New York, higher income pushes some dollars into much steeper brackets — up to 12.3% in California and 9.65% in New York for income over $1,077,550.
For a single filer earning $150,000:
- Illinois (4.95% flat): state tax ≈ $7,280
- California (progressive): state tax ≈ $9,561
- New York (progressive): state tax ≈ $8,291
At $80,000, the differences narrow because both the progressive and flat-tax states tax most income at moderate rates. See Highest State Income Tax Rates for the full progressive-state picture.
State-Level Changes to Watch
Several flat-tax rates changed recently:
- Arkansas cut its top rate from 3.9% to 3.7% effective January 1, 2026, under Acts 1 and 2 of the 2026 First Extraordinary Session. Arkansas remains a progressive state (not flat) but the direction of reform is down.
- Georgia adopted its flat 4.99% in prior legislation; the 2026 rate is confirmed.
- Iowa reduced its rate to 3.80% as part of a multi-year transition away from graduated brackets. The transition began in 2023 and the 3.80% flat rate is now in effect for 2026. (Iowa Code § 422.5)
- North Carolina dropped to 3.99% for 2026; S.B. 257 (July 2026) schedules further reductions beginning in 2027.
- Arizona enacted HB 4168 (Laws 2026, ch. 140, signed June 13, 2026), setting the flat rate at 2.5%. The Arizona Department of Revenue had not published the 2026 indexed standard deduction as of October 2026, so the AZ figures here carry low confidence.
State-specific calculators: Indiana · Illinois · Michigan · Massachusetts · Georgia · Pennsylvania · Kentucky