Illinois (IL) Quarterly Estimated Tax Calculator
Tax year: 2026 · Last updated 2026-06-22 · Source: IRS
Reviewed by CalcSumly Engineering Team, calculator authors and data architects · 2026-06-22
Your projected Schedule C net profit for the year.
W-2 wages, a spouse's income, interest, etc.
Federal tax withheld from a job or covered by credits.
Combined quarterly payment
$5,046
$16,647 federal + $3,535 IL state = $20,183 annual
Federal payment schedule
- Q1 · April 15, 2026$4,162
- Q2 · June 15, 2026$4,162
- Q3 · September 15, 2026$4,162
- Q4 · January 15, 2027$4,162
Add $884 IL state per quarter (equal installment approximation). Verify state schedule and forms at IL Dept. of Revenue — Income Tax Rates (4.95% flat rate).
How the Illinois quarterly estimated tax calculator works
This calculator estimates both federal and Illinois state quarterly tax obligations for a self-employed person in 2026.
Federal estimated tax
The federal calculation follows IRS Form 1040-ES: SE tax on 92.35% of net profit at 15.3%, reduced by the deductible half (reducing AGI), then federal income tax on taxable income (AGI minus standard deduction, minus optional QBI deduction). The result minus withholding is divided by 4 for equal quarterly installments due April, June, September, and January.
Illinois estimated tax
Illinois income tax is computed on adjusted gross income minus the Illinois standard deduction ($2,925 single / $5,850 MFJ).
The state quarterly payment shown is one-quarter of the annual state income tax — an equal-installment approximation. Verify your state's actual schedule and threshold at IL Dept. of Revenue — Income Tax Rates (4.95% flat rate).
Scope and limitations
Not included: Excludes Illinois local taxes and the 1.5% Personal Property Replacement Tax (PPRT) that applies to S-Corps and partnerships at entity level. SDI is not applicable in Illinois. Age-related additional exemption ($1,000 per qualifying condition) is excluded. State-specific credits, local income taxes, and penalties for underpayment are not modeled. The state estimated tax base may differ from the federal base in ways not captured here.
Use this for planning, not filing. Federal figures from IRS Rev. Proc. 2025-32; state figures from IL Dept. of Revenue — Income Tax Rates (4.95% flat rate) for 2026.
Sources
- IRS — Self-Employment Tax (Schedule SE)
- SSA — 2026 Social Security wage base ($184,500)
- IRS — Topic 751 Additional Medicare Tax
- IRS — Rev. Proc. 2025-32 (2026 inflation adjustments)
- IRS — Form 1040-ES (Estimated Tax for Individuals)
- IRS Notice 2025-67 — 2026 Retirement Plan Limits (§415, §402(g), §401(a)(17))
- IRS — SEP Contribution Limits 2026 ($72,000)
- IRS Notice 2026-10 — 2026 Standard Mileage Rates (72.5 cents/mile)
- IRS Rev. Proc. 2013-13 — Home Office Simplified Method ($5/sqft, 300 sqft max)
- IRS Publication 946 (2026) — Section 179 Deduction ($2,560,000 limit; $32,000 SUV cap)
- IL Dept. of Revenue — Income Tax Rates (4.95% flat rate)
- IL Dept. of Revenue — What is the Illinois exemption allowance? ($2,925 per exemption, 2026)
Frequently asked questions
Does Illinois require quarterly estimated tax payments?+
Yes. Illinois requires estimated income tax payments if you expect to owe at least $500 in IL income tax after withholding and credits. Illinois uses the same quarterly due dates as the federal schedule (April, June, September, January) and Form IL-1040-ES. The IL rate is a flat 4.95% on net income.
Do freelancers in Illinois owe state estimated taxes in addition to federal?+
Yes. Freelancers in Illinois who expect to owe more than $500 in state income tax (threshold varies; check with the Illinois Department of Revenue) are generally required to make quarterly estimated state tax payments. These are separate from your federal 1040-ES payments.
When are federal estimated tax payments due in 2026?+
Federal estimated tax payments for 2026 are due on: April 15 (Q1), June 16 (Q2, adjusted from June 15), September 15 (Q3), and January 15, 2027 (Q4). Missing a payment or underpaying may result in a penalty under IRS Form 2210, even if you pay in full by April 15.
How is the quarterly estimated tax amount calculated?+
The calculator estimates your annual tax liability: (1) SE tax on 92.35% of net profit × 15.3%; (2) federal income tax on taxable income (AGI minus standard deduction, minus optional QBI deduction); (3) state income tax using your state's rates and deduction rules. It then subtracts withholding and divides by 4 (federal) or applies the state's installment schedule.
What happens if I underpay federal estimated taxes?+
The IRS charges a penalty for underpaying estimated taxes (Form 2210). For 2026, the penalty rate is approximately 7–8%. To avoid the penalty, pay either 90% of this year's tax or 100% of last year's tax (110% if last year's AGI exceeded $150,000). Using the safe harbor based on last year's return is often the simplest approach for freelancers with variable income.
Should I pay estimated taxes monthly rather than quarterly?+
The IRS and most states require quarterly (not monthly) estimated tax payments. However, you can pay more frequently or in advance of due dates — overpaying is not penalized. Many freelancers find it easier to set aside a fixed percentage of each invoice payment and make monthly deposits, then ensure each quarterly deadline's cumulative amount meets the required installment.
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