Tax Filing Deadlines

Why This Matters

Tax filing deadlines aren't just arbitrary dates on a calendar—they're the backbone of the entire tax administration system. Understanding when different returns are due reveals why the system is structured the way it is: pass-through entities file first so their owners can report income on individual returns, employers report wages before employees file, and estimated payments keep revenue flowing throughout the year. You're being tested on your ability to connect these deadlines to broader concepts like entity classification, tax compliance, and cash flow management.

Don't just memorize a list of dates. Know which entities file when, why pass-through deadlines precede individual deadlines, and how extensions work differently for filing versus payment. The exam loves to test whether you understand that an extension to file is never an extension to pay—miss that distinction and you'll miss points.

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Information Reporting Deadlines

Before anyone can file a return, they need the documentation to do it accurately. Information returns flow from payers to recipients, creating the foundation for accurate tax reporting.

January 31 – W-2 and 1099 Deadline

• Employers must furnish W-2 forms to employees by this date, reporting wages and withholdings for the prior year
• 1099 forms for independent contractors and other payments are also due to recipients, enabling accurate income reporting
• Penalties for late issuance range from $\$50$ to $\$280$ per form, depending on how late—creating strong compliance incentives for employers

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Pass-Through Entity Deadlines

Pass-through entities file before individuals for a critical reason: their income flows through to owners' personal returns, so partners and shareholders need K-1s before they can file their own taxes.

March 15 – S Corporation Returns (Form 1120-S)

• S Corporations file Form 1120-S by March 15, reporting income that passes through to shareholders' individual returns
• Schedule K-1s must be issued to shareholders, detailing each owner's share of income, deductions, and credits
• Six-month extension available (to September 15), but any tax owed by shareholders should still be estimated and paid by April 15

March 15 – Partnership Returns (Form 1065)

• Partnerships file Form 1065 as an information return—the entity itself pays no tax, but must report all activity
• K-1 distribution to partners is essential for partners to accurately report their distributive share on personal returns
• Late filing penalty is $\$220$ per partner per month (2024), making timely filing especially costly for large partnerships

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Primary Return Deadlines

These are the dates most taxpayers think of as "tax day." Individual and C Corporation returns share the April 15 deadline, but for different structural reasons.

April 15 – Individual Returns (Form 1040)

• Primary deadline for federal individual income tax returns, covering wages, self-employment, investments, and all other income sources
• Payment is due regardless of filing—even if you request an extension, taxes owed must be paid by April 15 to avoid penalties and interest
• Automatic six-month extension available via Form 4868, but this only extends the filing deadline, not the payment deadline

April 15 – C Corporation Returns (Form 1120)

• Calendar-year C Corporations file Form 1120 by April 15, reporting corporate income taxed at the entity level
• Fiscal-year corporations file by the 15th day of the fourth month after their year-end—a common exam trap
• Estimated tax payments must be current; corporations owing $\$500$ or more must make quarterly deposits throughout the year

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Extended Filing Deadlines

Extensions give taxpayers more time to file, but never more time to pay. This distinction is heavily tested.

September 15 – Extended Pass-Through Deadline

• Final deadline for S Corps and Partnerships that filed for a six-month extension from the original March 15 date
• K-1s should have been issued earlier—waiting until September creates problems for individual filers who need this information
• No additional extensions available beyond this date; failure to file triggers automatic penalties

October 15 – Extended Individual Deadline

• Absolute final deadline for individual returns that received an April 15 extension
• Interest and penalties on unpaid taxes have been accruing since April 15, regardless of the filing extension
• No further extensions granted except in rare cases like combat zone service or federally declared disasters

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Estimated Tax Payment Deadlines

Self-employed individuals, investors, and others without sufficient withholding must pay taxes quarterly. The pay-as-you-go system prevents large year-end tax bills and keeps government revenue steady.

April 15 – Q1 Estimated Payment

• First quarterly payment due for taxpayers expecting to owe $\$1{,}000$ or more after subtracting withholding and credits
• Covers income from January through March, though payments are based on annual projections
• Safe harbor rule: pay 100% of prior year's tax (110% if AGI exceeds $\$150{,}000$) to avoid underpayment penalties

June 15 – Q2 Estimated Payment

• Second quarterly payment due, covering the April–May income period (note the uneven two-month period)
• Mid-year adjustment opportunity—taxpayers should reassess if income is higher or lower than projected
• Annualized income method available for those with uneven income to potentially reduce required payments

September 15 – Q3 Estimated Payment

• Third quarterly payment due, covering June through August income
• Critical for self-employed and gig workers whose income may fluctuate significantly quarter to quarter
• Coincides with pass-through extended deadline—busy date for tax practitioners

January 15 – Q4 Estimated Payment

• Final estimated payment for the prior tax year, covering September through December income
• Can be skipped if taxpayer files their return and pays all tax due by January 31
• Last chance to avoid underpayment penalty for the completed tax year

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Quick Reference Table

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Self-Check Questions

1. Why do S Corporations and Partnerships have a March 15 deadline while individuals file April 15? What document must flow from entity to owner?

2. A taxpayer files Form 4868 for an automatic extension. They owe $\$3{,}000$ but don't pay until October 15. What penalties and interest will they face, and why?

3. Compare the Q2 estimated payment period (April 15–June 15) to the Q3 period (June 15–September 15). Why aren't quarterly payments based on equal three-month periods?

4. An employer fails to send W-2 forms until March 1. How does this late issuance create a cascade of compliance problems for employees?

5. A C Corporation with a fiscal year ending June 30 needs to file its return. What is its filing deadline, and how does this differ from a calendar-year corporation?