Side-by-side at $1,000,000 qualified income, 37% bracket
| Field | Illinois | Wisconsin |
|---|---|---|
| Statute | 35 ILCS 5/201(p) (IL Income Tax Act PTE election); effective tax years ending on or after December 31, 2021 | Wis. Stat. § 71.21(6)(a) (partnership PTE election) and § 71.365(4m)(a) (S corp PTE election) |
| Election deadline | Annual election made on a timely-filed original Form IL-1065 or IL-1120-ST (including extensions). Election is irrevocable after the extended due date. | [PLACEHOLDER: state DOR cite] — exact election deadline mechanics (partnership Form 3 vs. S corp Form 5S) to be pinned in 2025 Form 3 / 5S instructions. |
| Rate | 4.95% flat | 7.90% flat |
| Owner credit | refundable | non-refundable |
| Composite interaction | stacks | stacks |
| §199A QBI reduction | Yes | Yes |
| Last verified | 2026-05-11 | 2026-05-11 |
Reference federal-arbitrage computation
Both scenarios assume $1,000,000 qualified net income, a 37% owner federal bracket, and no apportionment. Both reduce §199A QBI base proportionally; net benefit shown is the federal SALT-arbitrage less the rough QBI offset (~20% × bracket × entity tax).
Entity-level tax: $49,500. Net of QBI offset (~$3,663): $14,652.
Entity-level tax: $79,000. Net of QBI offset (~$5,846): $23,384.
Why owners with K-1 income across these two states care
Illinois and Wisconsin interact in three ways that matter to a multi-state K-1 holder: (1) independent elections — each state's PTET is its own election with its own deadline and form, so a missed IL deadline does not affect WI; (2) aggregate federal deduction — the entity-level tax paid to BOTH states is deductible at the federal entity level under IRS Notice 2020-75, so the federal arbitrage compounds; (3) composite-return interaction may differ — see each state's row above.
Run the multi-state picker pre-filled with both jurisdictions: