Illinois Estimated Quarterly Tax

Illinois requires estimated quarterly tax payments if you expect to owe more than $1,000 in state tax. The safe harbor is paying 90% of your current year tax liability or 100% of your prior year tax. Payments are due on the same dates as federal (April 15, June 15, September 15, January 15).

Why It Matters

Self-employed workers and freelancers in Illinois must make estimated quarterly payments for both federal and state taxes. Missing payments or underpaying can result in penalties from both the IRS and Illinois Department of Revenue. Illinois charges a 7.0% penalty rate on underpayments. Planning ahead helps you avoid surprises at tax time and manage cash flow throughout the year.

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How It Works

Illinois estimated tax is calculated on your expected state taxable income for the year. File using IL-1040-ES through Illinois Department of Revenue. Payments are divided equally (25% each quarter). Due dates are 2026-04-15, 2026-06-15, 2026-09-15, and 2027-01-15. The annualized income installment method is available for taxpayers with uneven income throughout the year.

Example

Single filer • $100,000 net SE income • 2026

Quarterly

$7,387

per quarter

Federal

$25,745

25.75%

Total Annual

$29,549

29.55%

Resources

Illinois Estimated Tax Payments - Official Portal

Official Illinois estimated tax payment portal administered by Illinois Department of Revenue.

Source: Illinois Department of Revenue

Frequently Asked Questions

Can I use the annualized income method in Illinois?

Yes. Illinois allows the annualized income installment method for taxpayers with income that varies significantly throughout the year (e.g., seasonal businesses). This method bases each installment on your actual income through that quarter, which can reduce early-year payments if most income arrives later.

How do I pay estimated taxes in Illinois?

You can make estimated tax payments in Illinois online through Illinois Department of Revenue's payment portal, by mailing IL-1040-ES with a check, or through electronic funds transfer. Online payment is the fastest and provides immediate confirmation.

What is the estimated tax threshold in Illinois?

Illinois requires estimated quarterly payments if you expect to owe more than $1,000 in state income tax after withholding and credits. This applies to self-employed individuals, freelancers, and anyone with significant non-wage income.

What is the penalty for underpaying estimated taxes in Illinois?

Illinois charges an underpayment penalty at a rate of 7.0% per year on the underpaid amount. To avoid penalties, pay at least 90% of your current year tax liability or 100% of your prior year tax (regardless of income level).

When are estimated tax payments due in Illinois?

Illinois follows the same due dates as federal estimated payments: April 15, June 15, September 15, and January 15. Payments are made using IL-1040-ES through Illinois Department of Revenue.