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IRS Tax Deadlines Every Business Owner Should Understand
What are the IRS tax deadlines every business owner should know?
The key IRS deadlines are: 1099 forms in January; partnership (Form 1065) and S-Corp (Form 1120-S) returns on March 15; individual (Form 1040) and C-Corp (Form 1120) returns plus the first estimated payment on April 15; and nonprofit Form 990 on May 15. Extensions push businesses to September 15 and individuals to October 15, but taxes owed are still due by the original deadline, so penalties and interest apply if you underpay.
If you’re a business owner or self-employed, IRS deadlines can get confusing fast.
There are different dates for personal returns, business returns, extensions, and estimated payments — and missing them can get expensive.
That’s why I sat down with tax resolution and tax planning expert Alexander Goussis to walk through the most common IRS deadlines and the mistakes people make every year.
Why IRS Deadlines Cause So Much Confusion
The IRS doesn’t operate on one simple calendar.
Deadlines vary based on:
- Business structure
- Whether you’re a pass-through entity
- Calendar year vs. fiscal year
- Whether you file an extension
Most issues don’t happen because people ignore taxes — they happen because people don’t realize which deadline applies to them.
Key IRS Filing Deadlines to Know
Here are the most common filing deadlines Alex and I discussed:
January
- 1099 forms must be issued and filed with the IRS
(https://www.irs.gov/forms-pubs/about-form-1099-nec)
March 15
- Partnerships (Form 1065)
- S-Corporations (Form 1120-S)
- Schedule K-1s must be provided to owners
These are pass-through entities, which is why the deadline comes earlier in the year.
(https://www.irs.gov/businesses/small-businesses-self-employed/business-structures)
April 15
- Individual tax returns (Form 1040)
- C-Corporations (Form 1120)
- First estimated tax payment for the year
This is also the deadline to pay taxes owed, even if you plan to file an extension.
(https://www.irs.gov/filing/individuals/when-to-file)
May 15
- Nonprofits filing Form 990 (calendar year entities)
(https://www.irs.gov/forms-pubs/about-form-990)
Calendar Year vs. Fiscal Year (Often Missed)
Most businesses operate on a calendar year (January 1 – December 31).
Some businesses elect a fiscal year, which changes their filing deadlines entirely.
In those cases, returns are generally due 3–4 months after the fiscal year ends.
If your business uses a fiscal year, it’s critical to confirm deadlines with your tax professional — assumptions here cause penalties.
Extension Deadlines (And the Big Misunderstanding)
Extensions give you more time to file, not more time to pay.
Here’s how extensions typically work:
Business Extensions
- March 15 → September 15 (Partnerships & S-Corps)
- Filed using Form 7004
(https://www.irs.gov/forms-pubs/about-form-7004)
Individual Extensions
- April 15 → October 15
- Filed using Form 4868
(https://www.irs.gov/forms-pubs/about-form-4868)
Why Extensions Can Still Cost You Money
This is where many people get caught.
Even if you file an extension:
- Taxes owed are still due by the original deadline
- Penalties and interest apply if you underpay
The IRS assesses:
- Failure-to-pay penalties
- Failure-to-file penalties
- Interest that compounds over time
This is why estimated quarterly payments matter so much for business owners.
(https://www.irs.gov/businesses/small-businesses-self-employed/estimated-taxes)
Watch the Full Conversation
In this video, we break down:
- Business vs. personal tax deadlines
- Extension deadlines and common mistakes
- Why paying late is more costly than people realize
- How better planning protects cash flow
Watch the full video here:
How to Get Clarity on Your Situation
Every business is different. Structure, profitability, and timing all matter.
If you’re unsure which deadlines apply to you — or you’re already behind — having a conversation early can help you avoid unnecessary penalties.
Alexander Goussis
Tax Resolution & Tax Planning Specialist
Freedom Tax Relief Services
Website: https://freedomtaxreliefservices.com
Phone: 516-708-6645
Email: alex@iraawaytoday.com
Final Thought
At Interconnect Mortgage, our goal is education and clarity.
Tax deadlines, business structure, and cash flow all impact long-term financial decisions — including homeownership and investing. Knowing the rules ahead of time gives you options.
If you want clarity on how taxes and income affect your financial or homeownership plans, the first step is a conversation — not pressure.
👉 Schedule a conversation here:
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Disclaimer:
This content is for educational purposes only and not a commitment to lend.
Interconnect Mortgage, a DBA of Palm Beach Mortgage Group Inc., NMLS 373094.
Licensed in Florida.
Check licensing at NMLS Consumer Access.
Frequently asked questions
Does filing a tax extension give me more time to pay? +
No. Extensions give you more time to file, not more time to pay. Taxes owed are still due by the original deadline, and if you underpay, the IRS assesses failure-to-pay penalties and interest that compounds over time.
When are business tax returns due to the IRS? +
Partnerships (Form 1065) and S-Corporations (Form 1120-S) are due March 15, along with Schedule K-1s for owners. C-Corporations (Form 1120) file by April 15, the same day as individual returns. Business extensions filed with Form 7004 move the deadline to September 15.
What if my business uses a fiscal year instead of a calendar year? +
A fiscal year changes your filing deadlines entirely. Returns are generally due 3-4 months after the fiscal year ends. If your business uses a fiscal year, confirm your exact deadlines with your tax professional, because assumptions here are what cause penalties.
What penalties does the IRS charge for missing a deadline? +
The IRS assesses failure-to-pay penalties, failure-to-file penalties, and interest that compounds over time. Even with an extension, penalties and interest apply if you underpay by the original deadline, which is why estimated quarterly payments matter so much for business owners.
About the author
Toni Taylor Gozza — Mortgage Expert
NMLS #274323
I'm Toni Taylor Gozza, a Mortgage Expert with Interconnect Mortgage in Palm Beach Gardens, Florida, NMLS #274323. I help self-employed borrowers, first-time buyers, and people with complex income or substantial assets explore mortgage options that fit how their finances actually work. My approach is education first: I explain the choices in plain English so you can make an informed decision without being pushed into a loan you don't need. Credentials: NMLS #274323; Interconnect Mortgage, a DBA of Palm Beach Mortgage Group Inc., NMLS #373094 Expertise: Non-QM & creative financing, asset depletion, self-employed borrowers, first-time buyers
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