The wrong assumption about your entity's deadline costs you a full month of penalties before you realize it. Here is the actual breakdown for every common business structure in 2026.
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Calendar-year filers using the 2026 deadlines. If you operate on a fiscal year, see the fiscal year rules further down.
| Entity | Form | Deadline | Extended |
| Single-member LLC | Schedule C (with 1040) | April 15, 2026 | October 15, 2026 |
| Multi-member LLC (partnership default) | Form 1065 + K-1s | March 16, 2026 | September 15, 2026 |
| LLC electing S-corp status | Form 1120-S + K-1s | March 16, 2026 | September 15, 2026 |
| LLC electing C-corp status | Form 1120 | April 15, 2026 | October 15, 2026 |
| S-corporation | Form 1120-S + K-1s | March 16, 2026 | September 15, 2026 |
| C-corporation | Form 1120 | April 15, 2026 | October 15, 2026 |
| General partnership | Form 1065 + K-1s | March 16, 2026 | September 15, 2026 |
| Limited partnership | Form 1065 + K-1s | March 16, 2026 | September 15, 2026 |
Source: IRS Publication 509, Tax Calendars (2026 edition). Extensions are obtained by filing Form 7004 by the original deadline.
The deadline shifts. The form changes. The K-1 obligations appear or disappear.
No separate business return. Income flows through to Schedule C on your personal 1040. Deadline is April 15, 2026. The LLC itself does not file at the federal level.
Files Form 1065 by March 16, 2026, plus a Schedule K-1 for every member. Each member uses the K-1 to file their personal return by April 15.
Files Form 1120-S and K-1s by March 16, 2026. Pass-through to shareholders, but the corporation itself is the filer. Late filings trigger the $245/shareholder/month penalty.
Files Form 1120 by April 15, 2026 and pays its own tax (no pass-through). Owners do not need K-1s. Common for businesses planning to reinvest profits or take outside investment.
Same rules as a multi-member LLC: Form 1065 and K-1s by March 16, 2026. The partnership entity is informational only; the tax is paid by the partners on their personal returns.
File by the 15th day of the 3rd month (S-corp, partnership) or 4th month (C-corp) after year-end. June 30 year-end C-corps file by September 15.
S-corps and partnerships file by March 16 because their owners need Schedule K-1 data to complete personal returns by April 15. The IRS staggers the deadlines to give the downstream filer a working month. If your S-corp files late, every shareholder is also late on their personal return, which is one reason the per-shareholder penalty is so steep.
C-corporations do not have this dependency. They pay their own tax at the corporate level and the only personal connection is dividends issued during the year, which are reported on Form 1099-DIV separately. That is why C-corps share the April 15 personal deadline rather than the earlier pass-through one.
Cross-reference the year-specific dates on the 2026 corporate tax deadline page, and see the corporate tax filing reminder if you want an email 60 days before whichever date applies to your entity.
It depends on how the LLC is taxed. Single-member LLCs file on the owner's personal return by April 15, 2026. Multi-member LLCs taxed as partnerships file Form 1065 by March 16, 2026. LLCs that elected S-corp status (Form 2553) file Form 1120-S by March 16, 2026. LLCs that elected C-corp status file Form 1120 by April 15, 2026.
Calendar-year C-corporations file Form 1120 by April 15, 2026. Fiscal-year C-corps file by the 15th day of the fourth month after their year-end. Corporations with a June 30 year-end have a special date: the 15th day of the third month after year-end (September 15).
S-corporations file Form 1120-S by March 16, 2026, plus Schedule K-1 for each shareholder. The statutory date is March 15, but it falls on a Sunday in 2026. Each K-1 is also a deliverable to shareholders by the same date so they can complete their personal returns.
Partnerships file Form 1065 by March 16, 2026, plus Schedule K-1 for each partner. The deadline matches the S-corp deadline because both are pass-through entities and their owners need K-1s to complete personal returns by April 15.
This is a structural question with tax implications beyond the deadline. S-corp election can save self-employment tax once profit clears roughly $40,000–$60,000 a year, but requires running payroll and filing Form 1120-S annually. C-corp election creates double taxation but allows reinvestment without owner self-employment tax. Talk to a CPA before electing.
Fiscal-year corporations file by the 15th day of the third month (S-corps, partnerships) or fourth month (C-corps) after the fiscal year ends. A corporation with a fiscal year ending June 30 files its S-corp return by September 15 and its C-corp return by September 15 (special June 30 rule) or October 15.
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