Form hub • IRS • Updated 2026
IRS 1120-S: S-Corp Return (K-1s + California 100S)
S-corporation annual return due March 15. Flows to shareholder K-1s; California mirrors with Form 100S at 1.5%.
Quick answers
- What is IRS 1120-S and when is it due?
- S-corporation annual return due March 15. Flows to shareholder K-1s; California mirrors with Form 100S at 1.5%. Due: March 15 (extendable to Sep 15).
Key facts
- California pair: Form 100S + 1.5% net-income tax ($800 min).
- Late cost: Federal per-shareholder, per-month penalty (inflation-indexed, about $250) + California entity penalties.
- Payroll proof: Reasonable-compensation W-2s must already exist: the return doesn’t create them.
Deadline
March 15 (extendable to Sep 15) (IRS). Extensions extend filing where offered — never payment.
Full walkthrough
IRS 1120-S is covered step by step, with worked examples, in S-corp payroll and reasonable compensation. For every deadline in the year, see the 2026 compliance calendar.
Other forms
FTB 3522 — due April 15FTB 3536 — due June 15FTB 568 — due Mar 15 (MMLLC) / Apr 15 (SMLLC)IRS 2553 — due 2 months 15 days into tax yearIRS 1120 — due April 15 (extendable to Oct 15)IRS 1065 — due March 15 (extendable to Sep 15)IRS 5472 — due April 15 with pro-forma 1120NY CT-3 — due April 15IRS SS-4 — due Before banking/hiringIRS W-9 — due Before first client paymentIRS 941 — due Quarterly (Apr/Jul/Oct/Jan)
Sources
- IRS form instructions; related guide on this site