If you earn 1099 or self-employment income in Illinois, the IRS and the state both expect you to pay taxes as you go — in four quarterly installments rather than one April bill. This calculator estimates your 2026 quarterly payments across all three pieces: federal self-employment tax, federal income tax, and Illinois state income tax. Illinois has a flat 4.95% income tax, so every dollar of your self-employment profit is taxed at the same state rate. Enter your expected net self-employment income, any W-2 wages, and your filing status to see what to send each quarter, your due dates, and how the safe-harbor rules protect you from an underpayment penalty. Everything is an estimate for planning — always confirm with the Illinois Department of Revenue before you file.
Self-employment income has no tax withheld for you, so both the IRS and Illinois Department of Revenue ask you to prepay in quarterly installments. On the federal side you owe self-employment tax (15.3% Social Security and Medicare on 92.35% of your net profit, up to the Social Security wage base) plus federal income tax on your profit after the standard deduction. On top of that, Illinois applies its own income tax.
Illinois generally requires estimated payments once you expect to owe more than $1,000 in state tax for the year. Illinois follows the federal schedule: April 15, June 15, September 15, and January 15. Illinois follows the standard four-installment schedule.
You avoid an IRS underpayment penalty by hitting a "safe harbor": paying at least 90% of this year's total tax, or 100% of last year's (110% if your income is higher). Illinois taxes your federal adjusted gross income at a flat 4.95%. It also allows a personal exemption allowance (about $2,850 per person) that is not reflected here, so your actual Illinois tax may be slightly lower. You can pay online through the Illinois Department of Revenue portal, and the calculator above breaks your total into the federal and Illinois pieces so you can send each to the right place. You can pay online at the Illinois Department of Revenue (payment portal).
For educational purposes only — not tax advice. Tax rules change and individual situations vary; confirm figures with a tax professional and the Illinois Department of Revenue before filing. State tax data last verified 2026-07-05.
Sources: tax.illinois.gov, tax.illinois.gov.