Illinois State Tax Guide
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Illinois State Tax Guide
Extension rules
Extension type: Automatic — no action required · IL-505-I (payment only)
Illinois grants an automatic 6-month extension to file — no form needed. Payment is still due April 15; use Form IL-505-I to submit an extension payment.
The Illinois extension extends the time to file, not the time to pay. Pay the balance due by the payment deadline to avoid penalties and interest.
Illinois Key deadlines (tax year 2025, return filed in 2026)
- Filing deadline: Apr 15, 2026
- Extension request deadline: Apr 15, 2026
- Extended return deadline: Oct 15, 2026
- Payment deadline: Apr 15, 2026
Interest and penalties accrue on any unpaid balance after this date, even with a valid extension.
Estimated payments
- Apr 15, 2026
- Jun 16, 2026
- Sep 15, 2026
- Jan 15, 2027
Payment rules
Pay any balance due to Illinois Department of Revenue (IDOR) by the payment deadline. Electronic payments post fastest; include the payment voucher when paying by check.
Payment options
- MyTax Illinois (bank transfer) · Free
- Credit card via ACI Payments · Processor fee applies
- Installment payment plan
Payment plan availability
Available: Yes
Installment payment plans are available by request through Illinois Department of Revenue (IDOR).
Filing forms
- IL-1040
- Schedule NR
Extension
- IL-505-I
Illinois Refund Tracking
Processing time: E-file: 4 weeks · Paper: 8–10 weeks
Do I need to file?
You generally must file a Illinois return if you are required to file a federal return and your Illinois-source income exceeds the state's filing thresholds.
- Residents: Illinois residents required to file a federal return generally must file Form IL-1040.
- Part-year residents: Part-year residents use Schedule NR with Form IL-1040.
- Nonresidents: Nonresidents with Illinois-source income use Schedule NR with Form IL-1040.
- Flat 4.95% state income tax rate on net income.
Official filing requirements — Illinois Department of Revenue (IDOR)
Thresholds change annually. Confirm your situation against current Illinois Department of Revenue (IDOR) guidance.
Filing methods
- E-file with FileTax
- E-file through an authorized provider or Illinois Department of Revenue (IDOR) online services
- Paper return by mail
