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As the 2025 tax season moves into its final phase, CPAs and accounting firms are preparing for one of the most critical deadlines of the year: the IRS tax extension deadline on September 15, 2025, applies to partnerships and S corporations that filed Form 7004. For individuals and corporations, this date also marks the third quarter estimated tax payment deadline not the extension filing deadline. While extensions give taxpayers more time to file, they also come with strict requirements, evolving IRS guidelines, and increased compliance risks.
For firms, this period is not just about paperwork. It is about safeguarding clients from late filing penalties, ensuring compliance with both federal and state tax rules, and staying ahead of IRS notices such as CP59 and CP59SN. With new provisions like disaster relief tax extensions, CPAs must approach this season with precision.
This guide from Unison Globus provides a clear breakdown of the IRS tax extension process for 2025, covering forms like Form 4868 for individuals and Form 7004 for businesses, key deadlines, common mistakes to avoid, and best practices for firms managing heavy extension workloads.
By following these guidelines, CPAs and EAs can ensure clients file accurately, minimize penalties, and maintain peace of mind before September 15.
What Is a Tax Extension?
A tax extension gives taxpayers additional time to file their return, but it does not extend the deadline for paying taxes owed. This distinction is where many clients get confused, and CPAS must explain the difference clearly.
The IRS provides two primary forms for filing an extension in 2025:
- Form 4868: For individual taxpayers who need extra time to file their personal income tax return.
- Form 7004: For businesses such as S-Corporations, Partnerships, and certain trusts that require more time to submit their returns.
When approved, an extension typically grants up to six additional months to file. However, all tax payments are still due by the original deadline, which is April 15 for individuals and March 17 for most businesses.
Failing to pay by the original deadline can trigger late payment penalties and interest, even if the return is filed on time after the extension. This is why CPAs should guide clients to make estimated payments alongside the extension request.
Key IRS Guidelines for 2025
Here are the critical updates CPAs and accounting firms must keep in mind for the 2025 extension season:
01. Final Federal Filing Deadlines
- October 15, 2025: Last date for individual taxpayers who filed Form 4868 to submit their extended 2024 income tax returns.
- September 15, 2025: Deadline for extended business returns filed with Form 7004, which applies to entities such as S Corporations and Partnerships.
02. Filing Preferences and Payment Reminders
- The IRS recommends e-filing with direct deposit because it reduces errors, shortens refund times, and provides digital confirmation of filing.
- An extension gives more time to file but not more time to pay. Taxes owed are still due by the original deadline of April 15, 2025, for individuals and March 17, 2025, for most businesses. Payments made after these dates may incur penalties and interest.
03. IRS Notices and Compliance Checks
- The IRS has started sending Notice CP59SN to taxpayers whose returns are not on file. CPAs should help clients verify whether their extension was received and respond quickly if action is required.
- In some cases, taxpayers may receive notice despite having filed correctly. CPAs can assist by checking IRS transcripts or e-Services and responding with proof of extension filing.
04. Disaster Relief Extensions
- The IRS continues to provide extra time for taxpayers in federally declared disaster areas. For instance, some affected regions now have deadlines extended into early 2026.
- A July 2025 tax relief law introduced a streamlined process that allows eligible individuals and businesses in disaster areas to automatically receive a 120-day postponement of filing and payment deadlines.
05. Heightened IRS Scrutiny
- The IRS has increased its focus on non-filers and late payers for the 2025 season. Penalties for late payment are typically 0.5 percent of the unpaid tax per month, up to 25 percent, and interest accrues until the balance is settled.
- CPAs should advise clients to make estimated tax payments when filing for an extension. Paying as much as possible by the original deadline helps reduce both penalties and interest.
Clarifying the September 15 Deadline: Extension vs. Estimated Payments
- For Businesses: September 15, 2025, is the final deadline for S Corporations and Partnerships that filed Form 7004 to submit their extended 2024 tax returns.
- For Individuals: This date is not the extension deadline. It is the third quarter estimated tax payment deadline for self-employed individuals, freelancers, and others with income not subject to withholding.
- For Corporations: Calendar-year C Corporations must also make their Q3 estimated tax payment by this date.
Reminder: The deadline to file an extended individual tax return is October 15, 2025, if Form 4868 was submitted by April 15.
Updated IRS Deadlines for 2025: What CPAs Must Know
The IRS has made key adjustments to 2025 tax deadlines that CPAs should be aware of:
| Entity Type | Form | Original Deadline | Extension Deadline | Change/Note |
|---|---|---|---|---|
| S Corporations | 1120-S | March 15, 2025 | September 15, 2025 | March 15 is a Saturday → deadline moved to March 17, 2025 |
| Partnerships | 1065 | March 15, 2025 | September 15, 2025 | Same as above |
| C Corporations | 1120 | April 15, 2025 | October 15, 2025 | No change |
| Individuals | 1040 + 4868 | April 15, 2025 | October 15, 2025 | No change |
| Multi-member LLCs | 1065 | March 15, 2025 | September 15, 2025 | Deadline moved to March 17 |
| Single-member LLCs | 1040 + Sch C | April 15, 2025 | October 15, 2025 | No change |
Note: These deadlines apply to calendar-year filers. Fiscal-year filers may have different due dates.
Also, under the July 2025 tax relief law, taxpayers in federally declared disaster areas automatically receive a 120-day extension for both filing and payment.
How CPAs Can Prevent Common Mistakes During Tax Extension Season
During extension season, errors are less about forms and more about habits. CPAs can prevent costly missteps by:
- Setting clear expectations: Many clients believe an extension solves everything. A quick upfront explanation prevents surprises about payments or penalties later.
- Providing estimated tax guidance: Even when documents are incomplete, offering a payment estimate reduces penalty exposure and eases client anxiety.
- Encouraging early action: Proactive outreach helps avoid the last-minute rush that often leads to missed deadlines or overlooked details.
- Standardizing communication on notices: A simple process for uploading IRS letters into a secure portal keeps nothing from slipping through the cracks.
- Monitoring multi-state clients: Centralized checklists help ensure that state-level filings and payments are handled alongside federal obligations.
Implementing these proactive steps can ensure smoother filing and prevent surprises for clients – making CPAs an indispensable resource during tax extension season. Reframing extension season as a proactive process helps CPAs keep clients compliant and reinforce their role as trusted advisors.
IRS Payment Options for Clients Who Owe
For many taxpayers, filing under extension does not eliminate the need to pay. If clients still owe taxes, CPAs can guide them through the following IRS-approved payment solutions:01. IRS Direct Pay
- A secure online tool that allows direct payments from a checking or savings account.
- No fees and immediate confirmation provided.
02. Electronic Federal Tax Payment System (EFTPS)
- A reliable option for businesses and frequent payers.
- Requires enrollment but allows scheduling future payments.
03. Online Payment Agreements
- Ideal for taxpayers unable to pay in full.
- Installment plans spread payments out and reduces the risk of enforced collection.
04. Short-Term Payment Extensions
- The IRS may grant up to 120 extra days to pay in full.
- Interest still accrues, but late payment penalties are reduced.
05. Credit or Debit Card Payments
- Payments can be made via IRS-authorized processors.
- Transaction fees apply but offer flexibility when other funds are tight.
Encouraging clients to pay as much as possible by the original deadline helps reduce penalties and interest. CPAs can play a proactive role by matching the right payment method to each client’s financial situation.
Need expert help with
your extension workload?
Unison Globus offers tailored CPA tax extension support with secure, scalable offshore staffing designed to ease peak-season pressures.
Contact Unison Globus today to discover how our offshore solutions can help your firm stay compliant, efficient, and stress-free this extension season.
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State vs. Federal Tax Extensions: What You Need to File on Time
A federal tax extension does not automatically apply at the state level. CPAs should be aware of the key differences:
| Aspect | Federal Tax Extension | State Tax Extension |
|---|---|---|
| Forms | Form 4868 (Individuals) and Form 7004 (Businesses) | Many states require their own extension forms, or accept the federal form (e.g., Form 4868 for individuals), but state-specific forms and processes must be checked. |
| Deadlines | September 15, for businesses (Form 7004) and October 15, for individuals (Form 4868) | State deadlines vary. While some states align with federal deadlines (e.g., September 15), others may have earlier or later due dates. CPAs should verify state-specific deadlines. |
| Payments | Taxes due by April 15 (individuals) or March 15 (businesses), even with an extension | State balances are calculated separately. Payments are generally due by the state’s original deadline, although some states may offer different rules for payment extensions or allow grace periods. |
| Automatic Coverage | Federal extension applies nationwide | Federal extension applies nationwide, but not all states accept it automatically. Separate state extension forms may be required. |
| Multi-State Clients | Single federal extension covers all taxpayers | CPAs must track each jurisdiction’s rules to ensure full multi-state tax compliance, as states may have different forms, deadlines, or rules. |
CPA Tip: Avoid confusion between the September 15 estimated tax payment deadline and the October 15 individual extension deadline. Many clients mistakenly believe they have until September 15 to file their personal returns, when in fact, this is the deadline for estimated tax payments for individuals. The actual deadline to file an extended individual return is October 15, 2025. Clear communication with clients is essential to prevent penalties for late filing or missed payments.
Best Practices for Accounting Firms During Extension Season
Managing the September 15 deadline can feel like a second peak of tax season. Firms that stay proactive and organized can reduce stress while improving client service. Here are key strategies:
- Communicate early and often: Remind clients about the upcoming deadlines and clarify what an extension does and does not cover.
- Use secure portals: Collect and share documents through encrypted platforms to avoid delays and protect client data.
- Standardize checklists: Maintain an internal CPA checklist for September 15 deadlines to track forms, payments, and state-level requirements.
- Prioritize complex clients: Handle multi-state or high-liability cases first to avoid bottlenecks later in the season.
- Leverage technology: Automation tools for reminders, e-filing, and document tracking can help streamline your accounting firm extension strategy.
- Consider outsourcing: Offshore tax preparation services allow firms to manage high volumes without sacrificing accuracy, especially when deadlines converge.
By following these best practices, firms can turn the extension season from a stress point into an opportunity to reinforce client trust and efficiency.
How Unison Globus Supports CPAs During Tax Extension Season
Tax extension season often feels like a second busy season, with heavy workloads and tight deadlines converging in August and September. This is where Unison Globus steps into provides comprehensive support for CPA firms across the U.S.
Our offshore teams specialize in:
- Expert tax preparation for forms including 1040, 1120, 1065, 1041, and 1099
- IRS-compliant documentation that minimizes errors and ensures smooth audits
- Secure, paperless workflows with encrypted client portals to streamline communication
- Scalable staffing models to help firms handle seasonal surges without increasing overhead
With offshore tax support for CPAs, firms gain the capacity to:
- Meet the September 15 tax extension deadline with confidence
- Reduce turnaround times during peak filing periods
- Stay compliant with both IRS extension filing 2025 requirements and state-level rules
- Focus more on advisory and client strategy instead of routine paperwork
At Unison Globus, we act as an extension of your firm, delivering the accuracy, efficiency, and peace of mind you need during one of the most demanding times of the year.
Final Thoughts:
Preparing for a Stress-Free Extension Season
As the September 15, 2025 tax extension deadline rapidly approaches, CPAs and accounting firms must act quickly to ensure clients remain compliant and avoid penalties. Staying ahead of IRS guidelines, tracking state-specific requirements, and advising clients on payment options are critical to managing this busy season effectively.
By focusing on clear communication, secure workflows, and well-organized checklists, firms can turn this high-pressure period into an opportunity to build stronger client relationships. Leveraging expert support, whether through advanced technology or specialized offshore teams – ensures that no return is missed and compliance remains intact.
