Washington Business Tax Extension 2026: 2025 Tax-Year Filing Guide
LLC & Partnership · S Corporation · C Corporation · Fiduciary
This guide explains how to file an Washington (WA) business tax extension for each entity type. For federal filing details, see our IRS Form 7004 business tax extension guide. Washington generally follows the corresponding federal filing and extension dates, while C corporations receive an additional one-month Washington filing period. Tax remains due by the original deadline.
Need a pro? Connect with a U.S.-based CPA or EA to prepare and file your Washington return.
Remember, payment is still due by the original deadline. In other words, extensions only extend filing time.
Washington (WA) rules depend on entity type. Next, confirm the entity’s classification, file the required extension or retain federal proof when applicable, and pay required tax by the original deadline.
Washington LLC & Partnership Tax Extension: Filing Details
A calendar-year partnership or LLC taxed as a partnership generally files Combined Excise Tax return, when a Washington filing obligation applies. For the 2025 calendar-year return, the extended filing deadline is Not applicable.
In addition, the extension applies to filing time only. Therefore, pay required Washington tax by the original deadline to limit penalties and interest.
The extension applies to filing time only. Pay required Washington tax by the original deadline to limit penalties and interest.
Washington S Corporation Tax Extension: Filing Details
For an S corporation, a calendar-year business generally files Combined Excise Tax return when it has a Washington filing obligation. For the 2025 calendar-year return, the extended filing deadline is Not applicable.
Washington C Corporation Tax Extension: Filing Details
For a C corporation, a calendar-year business generally files Combined Excise Tax return and must follow Washington corporate-income-tax extension rules. For the 2025 calendar-year return, the extended filing deadline is Not applicable.
The extension applies to filing time only. Pay required Washington tax by the original deadline to limit penalties and interest.
The extension applies to filing time only. Pay required Washington tax by the original deadline to limit penalties and interest.
Fiduciary, Estate, and Trust Filing Details
Finally, a calendar-year estate or trust generally files Combined Excise Tax return when it has a Washington fiduciary filing obligation. For the 2025 calendar-year return, the extended filing deadline is Not applicable.
Quick Reference: Deadlines and Forms
The table below provides a quick reference to Washington business tax extensions and return forms.
| Entity Type | Washington Return Form | Extension Method | Extended Deadline |
|---|---|---|---|
| LLC / Partnership | Combined Excise Tax return | federal Form 7004 | Not applicable |
| S Corporation | Combined Excise Tax return | federal Form 7004 | Not applicable |
| C Corporation | Combined Excise Tax return | federal Form 7004 | Not applicable |
| Fiduciary / Estate / Trust | Combined Excise Tax return | federal Form 8868 | Not applicable |
Frequently Asked Questions
Quick answers about Washington business tax extensions – but always confirm the current rules with the Washington Department of Revenue.
Visit WA DORYes. However, the applicable entity-specific requirements listed above must be satisfied. Washington grants extensions to LLCs, partnerships, S corporations, C corporations, and fiduciaries, but the rules – including which form to file, how long the extension lasts, and the payment threshold – vary by entity type. If you need an individual rather than business extension, see our Washington individual tax extension page.
Generally no. In other words, pay required tax by the original deadline and confirm the current state payment rules. An extension of time to file does not extend the time to pay – failing to pay by the original deadline can result in penalties and interest, even if the return is filed within the extended window.
No. Entity types use different Washington rules. For 2025 calendar-year returns filed in 2026, partnerships and S corporations generally use September 15; fiduciary returns generally use September 30; and C corporations generally use December 15 because Washington adds one month after the federal extended due date.
Review the Washington Department of Revenue guidance for the entity’s return. Additionally, the DOR publishes the most current forms (federal Form 7004, Federal Form 8868, etc.) and any changes to extension periods or payment thresholds.
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