IL-505-I: Automatic Extension Payment for Individuals Filing Form IL-1040 (2025)
Illinois · Illinois DOR · Used for tax years 2025
Form IL-505-I is Illinois’ automatic extension payment form for individuals filing Form IL-1040. It includes a worksheet to calculate tentative tax due and a voucher for payment by paper check or money order. The form is not required to obtain the automatic six-month filing exten
Who files this form
File Form IL-505-I only if all three apply:
- You cannot file your Illinois income tax return by the due date.
- You owe tentative tax, as calculated on the Tax Payment Worksheet.
- You pay by paper check or money order.
Do not file this form if no payment is due or you pay electronically, including by credit card. You do not need to file it to receive the automatic six-month filing extension.
When it's due
Tax year 2025: The form lists October 15 as the automatic extended filing date for calendar-year filers. It does not print the calendar year for that date or a specific original payment due date.
What you'll need
To complete the worksheet and payment voucher, have:
- Form IL-1040 to calculate expected income tax and other taxes.
- Your Illinois withholding amounts, including any 2025 pass-through withholding reported on Schedule K-1-P or K-1-T.
- Amounts of estimated payments, overpayments credited to 2025, and previous IL-505-I payments for 2025.
- Information about your estimated allowable tax credits.
- Your Social Security number, your spouse’s Social Security number if applicable, names, address, and daytime phone number.
- A check or money order if paying by mail.
If you file Form IL-1040 after the automatic six-month extension and the IRS granted an additional extension, attach a copy of the federal extension document to your return.
How to file
- Complete the Tax Payment Worksheet. Subtract Line 6 from Line 1 and round to whole dollars. Enter the result on Line 7 and the payment voucher.
- If the tentative tax due is $1 or more, pay that amount. If it is less than $1, do not file the form or make a payment.
- For payment by mail, complete and return only the bottom payment voucher with your check or money order. Keep the worksheet for your records.
Make your payment payable to Illinois Department of Revenue. Write your Social Security number, tax year, and “IL-505-I” on the payment. Mail it with the voucher to:
Illinois Department of Revenue
P.O. Box 19005
Springfield, IL 62794-9005
Submit the voucher and payment by the original due date of your annual return, or as soon as you realize you owe tentative tax.
Electronic payment: Visit mytax.illinois.gov to pay from a checking or savings account. You will need your IL-PIN. The form also lists credit card and electronic funds transfer options. Credit card payments carry a service-provider convenience fee. Do not file Form IL-505-I when paying electronically.
Common mistakes
- Treating the filing extension as extra time to pay. Tentative tax must be paid by the original return due date to avoid late-payment penalty and interest.
- Sending Form IL-505-I when no payment is due or when paying electronically or by credit card.
- Redacting Social Security numbers, which can delay processing. Enter the numbers in the same order as on your federal return.
- Forgetting to write your Social Security number, tax year, and “IL-505-I” on your check or money order.
- Forgetting to claim IL-505-I payments on 2025 Form IL-1040, Line 26.
Questions people ask
Do I need to request the six-month extension?
No. Illinois automatically grants a six-month extension to file. Form IL-505-I is not required to obtain it.
Can I get more than six months to file?
Illinois grants an extension beyond six months only if the IRS grants you an additional extension.
Should I attach an explanation for filing late?
If you file within the automatic six-month extension, do not attach anything explaining the delayed filing. If you file after that period with an additional IRS extension, attach the document granting that extension to avoid a late-filing penalty.
What penalties or interest could apply?
A late-filing penalty applies if you do not file a processable return by the extended due date. A late-payment penalty applies if you do not pay by the original due date. A bad-check penalty applies if your financial institution does not honor your payment. Interest runs from the day after the original due date through the payment date.