Illinois Quarterly Tax Calculator
Calculate your estimated quarterly tax payments for federal and Illinois state taxes. Designed for self-employed individuals, freelancers, and independent contractors.
IL State Tax: Flat 5.0%
Quarterly Payment Amount
$6,513
Per quarter (4 remaining)
Annual Tax Breakdown
2026 Payment Schedule
Jan 1 - Mar 31
Due: April 15, 2026
$6,513
Apr 1 - May 31
Due: June 15, 2026
$6,513
Jun 1 - Aug 31
Due: September 15, 2026
$6,513
Sep 1 - Dec 31
Due: January 15, 2027
$6,513
Don't miss your quarterly payments!
The IRS may charge penalties and interest if you underpay or pay late. Consider setting up automatic payments or calendar reminders.
Illinois Quarterly Tax Highlights
Illinois has a flat 4.95% income tax rate
Constitutional amendment requires flat rate
Use Form IL-1040-ES for quarterly payments
Simple flat rate for all income levels
Illinois Quarterly Tax FAQ
What is Illinois's income tax rate?
Illinois has a flat 4.95% income tax rate mandated by the state constitution. This applies equally to all income levels, making tax calculation straightforward.
Illinois Estimated Quarterly Tax Payments for Self-Employed Workers in 2026
Self-employed workers in Illinois face two tax obligations: federal estimated taxes filed with the IRS and state estimated taxes filed with the Illinois Department of Revenue. Illinois imposes a flat 4.95% income tax rate on all taxable income. If you expect to owe $1,000 or more in Illinois state income tax after withholding and credits, you must make quarterly estimated payments using Form IL-1040-ES.
Illinois's flat rate is constitutionally mandated. A 2020 ballot measure to allow progressive rates was rejected by voters. The 4.95% rate applies to all income levels equally, with no brackets or graduated rates.
| Tax Layer | Rate / Range | Filed With | Form |
|---|---|---|---|
| Federal income tax | 10% – 37% | IRS | 1040-ES |
| Self-employment tax | 15.3% | IRS | 1040-ES / SE |
| Illinois state income tax | 4.95% | Illinois Department of Revenue | Form IL-1040-ES |
How Illinois's Flat 4.95% Income Tax Affects Your Quarterly Payments
Illinois uses a flat tax rate of 4.95%, which simplifies quarterly tax calculations. Regardless of income level, every dollar of taxable income is taxed at the same rate. This makes it straightforward to estimate your state quarterly payments — simply multiply your projected net self-employment income by 4.95% and divide by four.
For a single self-employed worker in Illinois earning $100,000 in net self-employment income, the estimated annual tax breakdown is:
| Tax Component | Estimated Amount | Calculation Basis |
|---|---|---|
| Federal income tax | ~$11,600 | After $15,700 standard deduction, 2026 brackets |
| Self-employment tax | ~$14,130 | 15.3% on 92.35% of net earnings |
| Illinois state income tax | ~$4,950 | 4.95% flat rate |
| Total annual tax | ~$30,680 | |
| Quarterly payment | ~$7,670 | Total / 4 quarters |
State payments can be made online through the Illinois Department of Revenue portal at tax.illinois.gov, by mail with a Form IL-1040-ES voucher, or via electronic funds transfer where available.
Federal Self-Employment Tax and Quarterly Due Dates
All self-employed workers must pay federal self-employment (SE) tax of 15.3% on 92.35% of net earnings. This consists of 12.4% for Social Security (on earnings up to $184,500 in 2026) and 2.9% for Medicare (no cap). An additional 0.9% Medicare surtax applies to earnings above $200,000 (single filers).
Both Illinois and federal estimated tax payments follow the same quarterly schedule:
| Quarter | Income Period | Due Date |
|---|---|---|
| Q1 | January 1 – March 31 | April 15, 2026 |
| Q2 | April 1 – May 31 | June 15, 2026 |
| Q3 | June 1 – August 31 | September 15, 2026 |
| Q4 | September 1 – December 31 | January 15, 2027 |
To avoid underpayment penalties, pay at least 100% of your prior-year tax liability (or 110% if your AGI exceeds $150,000) spread across four equal payments, or at least 90% of your current-year tax. You can deduct 50% of your self-employment tax from your adjusted gross income, reducing both your federal and Illinois taxable income.
Related Calculators
Official References
This calculator uses current federal and Illinois tax rates and schedules:
- IRS Estimated Tax Guidelines
Federal quarterly tax requirements and Form 1040-ES
- Illinois Department of Revenue
Official Illinois tax authority
- IRS Self-Employment Tax
Social Security and Medicare tax information
This calculator provides estimates based on 2026 tax rates. Your actual tax liability may vary based on deductions, credits, and other factors. Consult a tax professional for personalized advice.