Illinois' Flat Tax Structure
Illinois levies a flat 4.95% income tax on federal AGI — with a few adjustments — for both employees and self-employed workers. There are no brackets, no progressive rate, no income-based phase-outs. A freelancer with $50,000 of net profit pays the same 4.95% marginal rate as a freelancer with $500,000. Voters rejected a graduated-rate amendment in 2020, and the flat structure has held since.
That flat rate is both Illinois' main pitch (simplicity) and its main criticism (regressive). For high-earning freelancers, 4.95% is a bargain compared to California's 13.3%. For low-earning freelancers, 4.95% on $30,000 of income hits harder than a bracketed rate that starts at 1% or 2%.
How Illinois Calculates Self-Employment Tax
Illinois starts from federal AGI and adds back a small list of items — most importantly, the federal Section 199A QBI deduction, federally tax-exempt income, and certain depreciation add-backs. The state does NOT add back the half of SE tax deducted on the federal return — that adjustment flows through unchanged. The result is the Illinois base income, which is then taxed at 4.95%.
A freelance developer with $120,000 of Schedule C profit, single, claims the federal standard deduction of $14,600 and a half-SE-tax deduction of about $9,200. Federal AGI lands near $96,200. Add back the QBI deduction of roughly $19,200 and Illinois base income rises to $115,400. State tax at 4.95% is about $5,700 — a clean number to model with the Self-Employment Tax Calculator.
| Illinois Taxable Income | State Tax at 4.95% |
|---|---|
| $30,000 | $1,485 |
| $75,000 | $3,713 |
| $150,000 | $7,425 |
| $300,000 | $14,850 |
| $500,000 | $24,750 |
Illinois Replacement Tax (PTRA)
Partnerships, S-corps, and trusts pay the Illinois Personal Property Replacement Tax (PTRA) at 1.5% of net income for partnerships and S-corps and 2.1% for trusts. Sole proprietors do not pay PTRA. A self-employed consultant who elects S-corp status pays Illinois 4.95% on wages and distributions plus 1.5% PTRA on the S-corp's net income — a meaningful cost when modeling whether the S-corp election pencils out.
Pass-Through Entity Tax (PTET) Election
Illinois offers a Pass-Through Entity Tax (PTET) election that lets partnerships and S-corps pay state income tax at the entity level rather than the owner level. The PTET rate is 4.95% — same as the individual rate — but the entity-level payment bypasses the federal $10,000 SALT cap. A partnership with $300,000 of pass-through income that elects PTET pays roughly $14,850 in Illinois tax at the entity level, fully deductible on the federal return. Without the election, the same income flows to the owners' personal returns where the SALT cap can swallow the deduction.
The PTET election is made annually on Form IL-1065 or Form IL-1120-ST and is binding for the year. Owners receive a credit on their personal IL-1040 for the PTET paid by the entity. The math is most powerful for owners with AGI above $200,000 — the SALT cap is fully consumed by property tax alone at that level, so any state income tax paid personally becomes non-deductible federally.
Chicago and Local Sales Tax
Illinois charges a 6.25% state sales tax on tangible goods. Local add-ons push the combined rate to 11% in parts of Chicago — the highest combined sales tax of any major U.S. city. Services are generally not taxable, but digital goods, SaaS, and computer software are taxed in many configurations. The economic nexus threshold is $100,000 of in-state sales or 200 separate transactions.
A freelancer selling digital templates into Illinois must register with the Illinois Department of Revenue once cumulative sales cross $100,000. Calculate the bite by destination with the Sales Tax Calculator — Illinois is an origin-based state for some transactions and destination-based for others, which trips up new sellers.
The Bottom Line
Illinois' flat 4.95% income tax is simple to model and competitive for high earners, though regressive at lower incomes. Sole proprietors pay only the flat tax; S-corps and partnerships also pay 1.5% PTRA on net income. Sales tax reaches 11% in Chicago with a $100,000 / 200-transaction nexus threshold. Project federal SE tax with the Self-Employment Tax Calculator and Illinois collection duties with the Sales Tax Calculator.