Quarterly Estimated Taxes in Illinois (2026)

flat / exact

Federal self-employment tax is the same in every state. What changes in Illinois is whether you also write a state estimated-income-tax check — and to whom. This page uses PiggyMath’s 2026 IRS / SSA figures and Illinois’s published flat / exact model. It is not a filed return.

By The PiggyMath Editorial Desk Last updated August 14, 2026

Federal 1040-ES dates (every state)

If you expect to owe at least $1,000 of federal tax, the IRS expects four estimated payments for income earned in 2026. The quarters are not equal: Q2 is only April–May; Q4 is four months.

Quarter	Income earned	Due
Q1	Jan 1 – Mar 31, 2026	April 15, 2026
Q2	Apr 1 – May 31, 2026	June 15, 2026
Q3	Jun 1 – Aug 31, 2026	September 15, 2026
Q4	Sep 1 – Dec 31, 2026	January 15, 2027

2027 federal dates (April 15, June 16*, September 15, January 18, 2028*) are on the deadlines hub. This page does not invent 2027 income-tax brackets. *Weekend/holiday shifts; confirm with the IRS.

Illinois estimates at a stable 4.95%

Illinois uses a constitutional-style flat 4.95% individual income tax. Planning percentages do not jump when profit crosses a bracket. PiggyMath treats IL as flat / exact: 4.95% of the profit proxy after the deductible half of SE tax.

IDOR estimated payments (typically Form IL-1040-ES) are separate from federal 1040-ES. Use MyTax Illinois, not IRS Direct Pay, for the state slice. The federal $1,000 rule is not Illinois’s estimated-tax trigger — check IDOR’s current instructions.

Chicago and some municipalities have other business fees; they are not a second personal income-tax bracket table. Do not confuse them with the 4.95% line. Leave the quarterly calculator’s state % at 4.95 for the income-tax set-aside, then add local fees only if you know they apply to your activity.

Agency: Illinois Department of Revenue. Source note: Illinois flat individual income tax 4.95%.

Worked set-aside: single filer, QBI on, Illinois

Illinois is modeled as a flat 5.0% of the profit proxy after the deductible half of SE tax (flat / exact). Locals, if any, are extra. Federal income tax uses the 2026 single brackets, standard deduction $16,100, and the simple QBI path (lesser of 20% of QBI and 20% of taxable income before the deduction) — the same simple path as the quarterly tax calculator.

Net profit	Federal SE tax	Federal income tax*	State (model)	Annual total	Each quarter
$40,000	$5,652	$1,775	$1,840	$9,267	$2,317
$80,000	$11,304	$5,344	$3,680	$20,328	$5,082
$120,000	$16,955	$11,506	$5,520	$33,982	$8,496

*After standard deduction and simple QBI. State column uses STATE_RATES_2026 (flat / exact) on profit after SE-half. Locals, AMT, and NIIT omitted. Not tax advice.

Worked example at $80,000

Federal SE tax: $11,304 (15.3% × 92.35% of profit; wage base $184,500)
Profit after deductible half of SE tax: $74,348
Simple QBI deduction used: $11,650
Federal income tax: $5,344
Illinois income tax (model): $3,680
Four equal federal+state planning checks: about $5,082 each (split the check: IRS Direct Pay vs Illinois Department of Revenue)

Safe harbor is federal-only until you read the state instructions: 90% / 100% / 110%. Lumpy income: Form 2210 annualized method.

Run the calculators with Illinois filled in

These links reopen the tools with this state’s planning inputs (shareable query string — nothing is uploaded).

Quarterly tax calculator — state % 4.95 at $80,000 profit (flat-rate field; Illinois may be graduated — prefer the estimator for brackets).
Freelancer tax estimator — IL selected, quality badge on the state line.
Deadline calendar (.ics) · 2026 tax constants

Frequently asked questions

Does Illinois follow the IRS quarterly dates?

Federal dates are April 15, June 15, September 15, and January 15 (next business day if needed). Illinois estimated income tax, if any, is a separate payment to Illinois Department of Revenue — confirm that calendar; do not treat federal safe harbor as a state safe harbor.

What is the federal $1,000 rule?

If you expect to owe $1,000 or more when you file Form 1040, the IRS generally expects 1040-ES installments. That trigger does not set your state’s estimated-tax threshold.

Can I skip Illinois estimates if I pay the IRS in full?

No. A federal payment does not credit Illinois. Pay Illinois Department of Revenue on its own vouchers when its rules say you must.

My freelance income is lumpy. Do I have to pay equal quarters?

Federally you can annualize on Form 2210. Equal 25% payments are the simple path. State annualization rules differ — check the agency instructions.

Sources

Figures reuse PiggyMath’s 2026 constants (Rev. Proc. 2025-32, SSA wage base $184,500, STATE_RATES_2026). Educational estimates — not tax advice. How we check our math →