07/28/2026
Illinois Estimated Tax Penalty
Did you recently get a Notice of Tax Due from Illinois?
You are generally required to make estimated tax payments to the state of Illinois if you expect to owe at least $1,000 in state tax for the year after accounting for any withholding and credits. This typically applies to taxpayers who receive income not subject to withholding, such as:
Out of State Workers
Self-employment income
Interest and dividends
Capital gains
Rental income
Business income from partnerships or S-corporations
If you did not pay enough tax throughout the year via withholding or estimated payments, you may owe a penalty even if you are due a refund.
Estimated payments are due in four equal installments (April 15, June 15, September 15, and January 15). If a quarterly payment is missed or short, the 2% or 10% late-payment penalty triggers based on when (and if) that specific quarter's balance gets resolved.
Staunton Accounting Services will give you estimated tax payment vouchers if requested.
It is hard to calculate the penalty accurately. The Illinois department of revenue calculates the penalty using the exact dates the State receives your payment. So we estimate your penalty based on the dates you mailed checks or electronically made payments to the Illinois Department of Revenue. With postage and processing time the dates can vary greatly. The amount we estimate is shown on page 2 of your Illinois 1040 line 34.
