The Illinois estimated tax form, IL-1040-ES, is what you use to calculate and pay state income tax on income that isn’t covered by employer withholding. You need it if your Illinois tax liability, minus withholding and credits, will exceed $1,000 for the year. The form contains a one-page worksheet to figure your annual tax at the flat 4.95% rate, plus four detachable vouchers for the quarterly installments.
Who Has to File It
Under 35 ILCS 5/803, estimated payments are required when the difference between your expected total Illinois tax and the amount already covered by withholding and credits is more than $1,000.1Illinois General Assembly. Illinois Compiled Statutes 35 ILCS 5/803 – Payment of Estimated Tax That’s a net figure, not a gross one. If your paycheck withholding is already large enough to keep the shortfall under $1,000, you don’t need to file the form even with side income.
Self-employed workers, gig workers, landlords, retirees drawing pension or investment income, and people with substantial dividends, interest, or capital gains are the usual filers. A quick check: pull your prior-year IL-1040. If you owed more than $1,000 at filing time and your situation hasn’t changed much, you probably need to make estimated payments this year.
Three groups are exempt. Farmers who earn at least two-thirds of their gross income from farming don’t have to make estimated payments. Neither do people age 65 or older who permanently live in a nursing home, or anyone who had no filing requirement in the prior year.2Illinois Department of Revenue. Publication 105 – Illinois Estimated Payments Requirements for Individuals and Businesses
Filling Out the Worksheet
Form IL-1040-ES is a PDF on the Illinois Department of Revenue website. The first page is the worksheet; the rest is the four vouchers.
The worksheet has you estimate your Illinois base income for the year, subtract exemptions, and multiply the result by 4.95% to get your expected total tax.3Illinois Department of Revenue. IL-1040-ES Estimated Income Tax Payments for Individuals 2026 Subtract any Illinois withholding you expect from wages and any credits you plan to claim. If what’s left is over $1,000, divide it by four. That’s the amount you write on each voucher.
Each voucher asks for your name, address, Social Security number in the same order it appears on your annual IL-1040, and the payment amount for that quarter.3Illinois Department of Revenue. IL-1040-ES Estimated Income Tax Payments for Individuals 2026 A transposed digit in the SSN can send your payment to the wrong account.
Quarterly Due Dates
Illinois follows the federal quarterly schedule. For the 2026 tax year, the installments are due:
- First quarter: April 15, 2026
- Second quarter: June 15, 2026
- Third quarter: September 15, 2026
- Fourth quarter: January 15, 2027
If a due date lands on a weekend or legal holiday, the payment is timely as long as it arrives by the next business day.4Illinois Department of Revenue. Pub-105 – Illinois Estimated Payments Requirements for Individuals and Businesses You can also pay the whole year’s estimated tax with your first installment in April if you’d rather be done with it.3Illinois Department of Revenue. IL-1040-ES Estimated Income Tax Payments for Individuals 2026
How to Submit Payment
Three options, all credited the same way.
Online Through MyTax Illinois
The MyTax Illinois portal transfers funds electronically from a checking or savings account.5Illinois Department of Revenue. Make a Payment – Options for Individuals Pick the correct tax year, enter the amount, and save the confirmation number. No paper voucher is needed when you pay online.
Credit or Debit Card
Visa, Mastercard, Discover, and American Express are accepted through three authorized processors, each charging a convenience fee of roughly 2.25% of the payment.6Illinois Department of Revenue. Pay by Credit Card On a $2,000 payment that’s about $45. Debit card fees can be lower depending on the processor.
Detach the current quarter’s voucher and mail it with a check or money order payable to the Illinois Department of Revenue. Write your Social Security number on the check so it gets credited correctly. The address on the voucher is:
Illinois Department of Revenue
Springfield, IL 62736-0001
Safe Harbors That Prevent a Penalty
Illinois won’t penalize you for underpaying if your installments meet one of two thresholds: 90% of your current-year liability, or 100% of your prior-year liability paid in four equal, timely installments.2Illinois Department of Revenue. Publication 105 – Illinois Estimated Payments Requirements for Individuals and Businesses The statute defines the required annual payment as the lesser of those two figures.7Illinois General Assembly. Illinois Compiled Statutes 35 ILCS 5/804 – Failure to Pay Estimated Tax
The prior-year method is the simpler one when your income swings. Take last year’s total Illinois tax, divide by four, and pay that each quarter. Even if this year’s tax turns out much higher, you won’t owe a penalty as long as you covered 100% of last year on time. Unlike the federal system, Illinois does not raise the threshold to 110% for high earners. The 100% rule applies at every income level.
You also owe no penalty if you had no Illinois tax liability in the prior year and that year was a full 12 months.7Illinois General Assembly. Illinois Compiled Statutes 35 ILCS 5/804 – Failure to Pay Estimated Tax
What Happens If You Underpay
Miss an installment or pay less than the required amount without qualifying for safe harbor, and Illinois assesses a late-payment penalty on the shortfall. The rate is 2% if paid within 30 days of the due date and 10% if paid more than 30 days late.8Illinois Department of Revenue. IL-2210 Computation of Penalties for Individuals The penalty applies quarter by quarter, so missing one deadline doesn’t automatically taint the others.
The calculation is based on the gap between what you should have paid and what you actually paid by the deadline. Required installment of $1,500, actual payment of $1,000, penalty runs on the $500 shortfall. You can compute it yourself on Form IL-2210, or wait for the Department of Revenue to send a notice.
If Your Income Is Uneven
Four equal installments work fine when your income is steady. When most of your money arrives in one season, equal installments can mean overpaying early and needing the annualized income installment method to avoid penalties on the light quarters.
Illinois allows the annualized method under 35 ILCS 5/804(c)(2).7Illinois General Assembly. Illinois Compiled Statutes 35 ILCS 5/804 – Failure to Pay Estimated Tax You figure actual income through each cutoff period, annualize it, and base the installment on that. The applicable percentages are 22.5% for the first quarter, 45% for the second, 67.5% for the third, and 90% for the fourth.8Illinois Department of Revenue. IL-2210 Computation of Penalties for Individuals Any reduction in one quarter gets recaptured, meaning the next required installment goes up by what you saved. Most tax software runs the calculation if you flag the option. If you do it by hand, keep the worksheets, because the Department can ask to see them.
Reporting the Payments on Your IL-1040
When you file your annual IL-1040, there’s a dedicated line for estimated payments made during the year. Everything you sent through vouchers, MyTax Illinois, or card counts toward tax already paid. If your estimated payments plus withholding come in over your actual liability, you get a refund or can apply the overpayment forward to next year’s estimates. If they come in under, the balance is due at filing.