Key tax deadlines for C-corporations and S-corporations in 2025:
February 28, 2025: Form 3921 (Mail Submission)
Who is required to file?
Corporations where employees exercised an Incentive Stock Option (ISO) during the tax year must submit Copy A of Form 3921 for each employee who exercised an ISO.
PTC insight:
- Form 3921 is not required for nonresident alien employees who exercised ISOs but do not receive a W-2 form.
- This deadline applies to forms filed via mail. For electronic submissions, the due date is March 31, 2025 (see below).
- Late filings result in penalties starting at $60 per form if the delay is within 30 days, with higher penalties for longer delays.
March 17, 2025: Form 1120-S (S-Corporations)
Who is required to file?
S-corporations using a fiscal year ending December 31 must submit Form 1120-S by this date. Deadlines may vary for fiscal years ending on other dates—consult IRS guidelines for specific information.
PTC insight:
- S-corporations can apply for an extension until September 15, 2025, by filing Form 7004 (Application for Automatic Extension of Time To File Certain Business Income Tax, Information, and Other Returns) on or before the original filing deadline.
March 31, 2025: Form 3921 (Electronic Submission)
Who is required to file?
Corporations where employees exercised ISOs during the tax year must electronically file Copy A of Form 3921 for each employee.
PTC insight:
- Form 3921 is not required for nonresident alien employees who exercised ISOs but do not receive a W-2 form.
- To file electronically, corporations must first obtain a Transmitter Control Code (TCC) from the IRS, which is required to use the Filing Information Returns Electronically (FIRE) system. The process of obtaining a TCC can take several weeks, so early preparation is advised.
- Penalties for late submissions begin at $60 per form if filed within 30 days after the deadline, with increased penalties for greater delays.
April 15, 2025: Form 1120 (C-Corporations)
Who is required to file?
C-corporations with a fiscal year ending December 31 must file Form 1120 by this date.
PTC insight:
- For C-corporations with fiscal years ending on dates other than December 31, the IRS provides alternate deadlines.
- Extensions are available by filing Form 7004 by the original filing deadline, allowing additional time to submit the return.
These deadlines are critical for compliance. Missing them can result in penalties and additional complications for businesses and their employees.
LLC tax deadlines
March 15, 2025: Form 1065
Who needs to file?
LLCs classified as domestic partnerships, along with other partnerships, must submit Form 1065 by this date.
PTC insight:
- Partnerships, including LLCs taxed as partnerships, don’t pay taxes directly on their income. Instead, profits or losses are passed through to the partners, who report these amounts on their individual tax returns.
- Extensions are available. By submitting Form 7004 (Application for Automatic Extension of Time To File Certain Business Income Tax, Information, and Other Returns) on or before March 15, LLCs can extend the filing deadline to September 15, 2025.
March 17, 2025: Schedule K-1 Distribution
Who needs to distribute?
LLCs and other pass-through entities must provide Schedule K-1 forms to their partners or members by this date.
PTC insight:
- As pass-through entities, LLCs do not pay income tax themselves. Instead, income, losses, credits, and deductions are allocated to individual members or partners, who report this information on their own tax returns.
- Schedule K-1 provides each partner’s or member’s share of the partnership’s income, losses, deductions, and credits for the tax year.
- The deadline for distributing K-1s is March 17, 2025, unless an extension for filing Form 1065 has been requested, in which case the distribution deadline is extended to September 15, 2025.
Note:
While there is no fixed deadline for issuing Schedule K-1s, they must be distributed once Form 1065 is completed and filed, with March 15, 2025, being the standard timeline.
Tax deadlines for sole proprietors
April 15, 2025: Schedule C (Form 1040)
Who is required to file?
Individuals operating as sole proprietors must complete and file Schedule C (Form 1040) to report the income or loss from their business or professional practice.
What qualifies as a business?
An activity is considered a business if:
- The primary goal is to earn income or make a profit.
- You participate in the activity on a consistent and ongoing basis.
PTC insight:
Sole proprietors must ensure their Schedule C is included with their individual tax return by the deadline to remain compliant with IRS regulations.
Need help preparing your taxes?
Schedule a free consultation with Konstantin to review your tax filings and ensure compliance. Let us help you navigate your taxes with confidence.
