Form 1120-S — S-Corporation Annual Return
Annual federal income tax return for US S-corporations. Due 15 March for calendar-year filers. 6-month automatic extension via Form 7004 to 15 September.
Finn tracks your United States deadlines
AccountsOS handles tax, filing deadlines and invoicing for United States businesses, in plain English. Ask Finn about yours, no signup needed.
Who this applies to
- All US S-corporations (entities that elected S status via Form 2553)
- LLCs taxed as S-corps after Form 2553 election
What to file
Form 1120-S with K-1s for each shareholder, P&L, balance sheet, M-1 reconciliation, basis tracking schedules.
How to file
Electronically via authorized e-filers. Send each shareholder their K-1 by 15 March (so they can file personal returns by 15 April).
Payment due
S-corp doesn't pay federal income tax (pass-through). Shareholders pay tax on their K-1 portion via personal Form 1040.
Penalties for missing this deadline
Late filing penalty: $245 per shareholder per month, max 12 months. Late K-1 distribution to shareholders has a separate $310 penalty per K-1.
Filing checklist
- Confirm reasonable compensation paid to shareholder-employees as W-2 wages
- Reconcile book to tax (Schedule M-1)
- Update shareholder basis schedules
- Generate K-1 for each shareholder
- Distribute K-1s by 15 March
- File Form 1120-S electronically
Common mistakes to avoid
- Under-paying owner W-2 wages (the #1 IRS S-corp audit issue)
- Forgetting state S-corp tax (some states tax S-corps directly)
- Missing the K-1 distribution deadline ($310 per K-1 penalty)
- Not tracking basis — affects future distributions and loss deductions
Never miss a United States deadline
AccountsOS tracks every Internal Revenue Service (IRS) and State Secretary of State (varies by state) deadline and reminds you weeks ahead.
Try Free