Check our 2026 Tax Deadlines For C-Corp Startups or Click for your customized tax compliance calendar by startup hub
For companies in Seattle, the most important tax deadlines (beyond the April 15th state and federal filing deadlines) are the February 1st Seattle business license tax dates (plus their quarterly follow-ons) and the quarterly Washington State excise tax due dates. See other important dates in the calendar below.
Washington Q4 2024 (for Quarterly Filers) Excise Tax Return (Business & Occupation Tax, Sales Tax & Use Tax)
Seattle 2024 Business License Tax deadline for annual filers (gross receipts between $100,000 to $200,000).
Washington Q4 State Fund Quarterly Report (Payroll Tax)
Seattle Q4 Business License Tax for Quarterly Filers (gross receipts more than $200,000).
Claim Research & Development Tax Credits on Form 941, and file annual Federal Unemployment Tax Act (FUTA) return on Form 940. Use our handy calculator to estimate your possible research and development tax credit.
Seattle startups should send 1099s to contractors. Send W2s to employees and e-file 1099-MISC for non-employee compensation with the IRS. Or file Form 8809 for a 30-day extension to file W2s and 1099-MISC for non-employee compensation.
Delaware Annual Franchise Report filing deadline. Your Seattle startup will pay a minimum of $400, which increases if you have significant funding.
For Seattle startups, IRS ACA Compliance 1094-B, 1095-B, 1094-C, and 1095-C filings are due (if paper-filing, due April 1 if eFiling). File Form 8809 for a 30-day extension.
Send 1095-B and 1095-C forms to employees.
IRS 30-day automatic extension: provide Form 1095-B and Form 1095C to employees.
IRS ACA Compliance 1094-B, 1095-B, 1094-C, and 1095-C filings are due (e-file).
Washington Annual 2023 Excise Tax Return (Business & Occupation Tax, Sales Tax & Use Tax)
C Corp Form 1120 Tax Return due. The Federal Form 1120 is the U.S. Corporation Income Tax Return, which the IRS has companies use to report their income, losses, credits, etc., and to figure the income tax liability of the corporation. Can extend the deadline to Oct. 15. All Seattle startups are required to file this Federal form by this deadline unless they file an extension.
Federal Quarterly Estimated Tax 1st installment (first quarter 2026).
File the R&D Tax Credit Form 6765 with your tax return. Can extend to October 15. We strongly recommend working with a qualified CPA to prepare this form in conjunction with your Form 1120 if your company is going to be acquired by a major technology company, that company’s CFO will use a strong tax team to do due diligence on this.
Due date for Seattle startup employees to make contributions to Individual Retirement Accounts (IRAs) for 2025 (Employee Benefits).
Seattle Q1 Business License Tax for Quarterly Filers.
Washington Q1 State Fund Quarterly Report Payroll Tax) due.
Washington Q1 Excise Tax Return due date.
Washington Personal Property Tax Listing Form and 50% of property taxes are due on this tax deadline.
Seattle startups can claim Research & Development Tax Credits on Form 941.
Delaware Quarterly Estimated Franchise Tax. Pay 40% of estimated annual amount (if annual amount expected to exceed $5,000).
Federal Quarterly Estimated Tax 2nd installment (second quarter 2026).
Seattle Q2 Business License Tax for Quarterly Filers
Washington Q2 State Fund Quarterly Report (Payroll Tax) due.
Washington Q2 Excise Tax Return due.
Claim Research & Development Tax Credits on Form 941.
Delaware Quarterly Estimated Franchise Tax. Pay 20% of your estimated annual amount (if annual amount expected to exceed $5,000).
Federal Quarterly Estimated Tax 3rd installment (third quarter 2026).
C Corp Form 1120 Tax Return final due date for Seattle startups if extension was filed.
Washington Q3 Excise Tax Return due.
Seattle Q3 Business License Tax for Quarterly Filers.
Remaining 50% of Washington Personal Property Tax due.
Washington Q3 State Fund Quarterly Report (Payroll Tax) due.
Claim your Research & Development Tax Credits on Form 941.
Delaware Quarterly Estimated Franchise Tax, Pay 20% of estimated annual amount (if annual amount expected to exceed $5,000).
Renew your business license annually (Seattle and Washington business licenses must be renewed by December 31 each year).
Federal Quarterly Estimated Tax 4th installment (fourth quarter 2026).
Click The Links To Learn More About These Filings And 2026 Seattle Startup Tax Deadlines
Federal Quarterly Estimated Tax 4th installment (fourth quarter 2025).
Washington Q4 2024 (for Quarterly Filers) Excise Tax Return (Business & Occupation Tax, Sales Tax & Use Tax)
Seattle 2024 Business License Tax deadline for annual filers (gross receipts between $100,000 to $200,000).
Washington Q4 State Fund Quarterly Report (Payroll Tax)
Seattle Q4 Business License Tax for Quarterly Filers (gross receipts more than $200,000).
Claim Research & Development Tax Credits on Form 941, and file annual Federal Unemployment Tax Act (FUTA) return on Form 940. Use our handy calculator to estimate your possible research and development tax credit.
Seattle startups should send 1099s to contractors. Send W2s to employees and e-file 1099-MISC for non-employee compensation with the IRS. Or file Form 8809 for a 30-day extension to file W2s and 1099-MISC for non-employee compensation.
Delaware Annual Franchise Report filing deadline. Your Seattle startup will pay a minimum of $400, which increases if you have significant funding.
For Seattle startups, IRS ACA Compliance 1094-B, 1095-B, 1094-C, and 1095-C filings are due (if paper-filing, due April 1 if eFiling). File Form 8809 for a 30-day extension.
Send 1095-B and 1095-C forms to employees.
IRS 30-day automatic extension: provide Form 1095-B and Form 1095C to employees.
IRS ACA Compliance 1094-B, 1095-B, 1094-C, and 1095-C filings are due (e-file).
Washington Annual 2023 Excise Tax Return (Business & Occupation Tax, Sales Tax & Use Tax)
C Corp Form 1120 Tax Return due. The Federal Form 1120 is the U.S. Corporation Income Tax Return, which the IRS has companies use to report their income, losses, credits, etc., and to figure the income tax liability of the corporation. Can extend the deadline to Oct. 15. All Seattle startups are required to file this Federal form by this deadline unless they file an extension.
Federal Quarterly Estimated Tax 1st installment (first quarter 2026).
File the R&D Tax Credit Form 6765 with your tax return. Can extend to October 15. We strongly recommend working with a qualified CPA to prepare this form in conjunction with your Form 1120 if your company is going to be acquired by a major technology company, that company’s CFO will use a strong tax team to do due diligence on this.
Due date for Seattle startup employees to make contributions to Individual Retirement Accounts (IRAs) for 2025 (Employee Benefits).
Seattle Q1 Business License Tax for Quarterly Filers.
Washington Q1 State Fund Quarterly Report Payroll Tax) due.
Washington Q1 Excise Tax Return due date.
Washington Personal Property Tax Listing Form and 50% of property taxes are due on this tax deadline.
Seattle startups can claim Research & Development Tax Credits on Form 941.
Delaware Quarterly Estimated Franchise Tax. Pay 40% of estimated annual amount (if annual amount expected to exceed $5,000).
Federal Quarterly Estimated Tax 2nd installment (second quarter 2026).
Seattle Q2 Business License Tax for Quarterly Filers
Washington Q2 State Fund Quarterly Report (Payroll Tax) due.
Washington Q2 Excise Tax Return due.
Claim Research & Development Tax Credits on Form 941.
Delaware Quarterly Estimated Franchise Tax. Pay 20% of your estimated annual amount (if annual amount expected to exceed $5,000).
Federal Quarterly Estimated Tax 3rd installment (third quarter 2026).
C Corp Form 1120 Tax Return final due date for Seattle startups if extension was filed.
Washington Q3 Excise Tax Return due.
Seattle Q3 Business License Tax for Quarterly Filers.
Remaining 50% of Washington Personal Property Tax due.
Washington Q3 State Fund Quarterly Report (Payroll Tax) due.
Claim your Research & Development Tax Credits on Form 941.
Delaware Quarterly Estimated Franchise Tax, Pay 20% of estimated annual amount (if annual amount expected to exceed $5,000).
Renew your business license annually (Seattle and Washington business licenses must be renewed by December 31 each year).
Federal Quarterly Estimated Tax 4th installment (fourth quarter 2026).
Note: The federal tax deadline this year is on April 15. The federal extension deadline for 2026 is October 15. When the tax deadline is on weekend or holiday, the deadline is moved to the next business day.
How Much Does a Startup Tax Return Cost? Try Kruze Consulting’s Tax Preparation Pricing Tool.
If your Delaware C-Corp Seattle funded startup needs tax help contact us today!
Seattle continues to ascend as a premier global tech and innovation hub for startups in 2026, now ranked #15 worldwide and #5 in the U.S. startup ecosystem. With an ecosystem valued at over $90 billion, Seattle is home to more than 1,500 active startups – especially strong in AI, healthtech, energy and environment, fintech, and software. Large anchor tech companies, a rich pool of technical talent, and dynamic university-industry collaborations, including the University of Washington’s Global Innovation Exchange, help drive new company formation and access to capital.
Early-stage investment and angel capital remain robust even as sectors evolve, and Seattle’s community of 25 unicorns (worth more than $49 billion) signals the city’s growing track record of success and exits. Founders benefit from strong networking via organizations like Techstars, Madrona, and the Washington Technology Industry Association, which all support early growth and specialized sector accelerators.
Tax and compliance obligations in Seattle remain central for founders:
Key 2026 tax deadlines include the February 1st business license tax (with follow-on quarterly filings), quarterly Washington excise tax, the standard April 15th federal and state tax filings (extendable to October 15th), and payroll as well as R&D tax credit reporting. Staying on top of these dates is essential for maintaining compliance and eligibility for special incentives.
Seattle’s combination of elite technical talent, infrastructure, and a culture of invention make it a compelling choice for ambitious startup founders in 2026.
2025 startup tax deadlines are supplied for reference purposes only, and should not be used when making decisions in 2026 or beyond. Always consult your tax professional, and see our disclaimer below.
Click The Links To Learn More About These Filings And 2025 Seattle Startup Tax Deadlines
Washington Q4 2024 (for Quarterly Filers) Excise Tax Return (Business & Occupation Tax, Sales Tax & Use Tax)
Seattle 2024 Business License Tax deadline for annual filers (gross receipts between $100,000 to $200,000).
Washington Q4 State Fund Quarterly Report (Payroll Tax)
Seattle Q4 Business License Tax for Quarterly Filers (gross receipts more than $200,000).
Claim Research & Development Tax Credits on Form 941, and file annual Federal Unemployment Tax Act (FUTA) return on Form 940. Use our handy calculator to estimate your possible research and development tax credit.
Delaware Annual Franchise Report filing deadline. Your Seattle startup will pay a minimum of $400, which increases if you have significant funding.
IRS 30-day automatic extension: provide Form 1095-B and Form 1095C to employees.
Washington Annual 2023 Excise Tax Return (Business & Occupation Tax, Sales Tax & Use Tax)
C Corp Form 1120 Tax Return due. The Federal Form 1120 is the U.S. Corporation Income Tax Return, which the IRS has companies use to report their income, losses, credits, etc., and to figure the income tax liability of the corporation. Can extend the deadline to Oct. 15. All Seattle startups are required to file this Federal form by this deadline unless they file an extension.
Federal Quarterly Estimated Tax 1st installment (first quarter 2024).
File the R&D Tax Credit Form 6765 with your tax return. Can extend to October 15. We strongly recommend working with a qualified CPA to prepare this form in conjunction with your Form 1120 if you are a high-growth startup – if your company is going to be acquired by a major technology company, that company’s CFO will use a strong tax team to do due diligence on this.
Due date for Seattle startup employees to make contributions to Individual Retirement Accounts (IRAs) for 2023 (Employee Benefits).
Seattle Q1 Business License Tax for Quarterly Filers.
Washington Q1 State Fund Quarterly Report Payroll Tax) due.
Washington Q1 Excise Tax Return due date.
Washington Personal Property Tax Listing Form and 50% of property taxes are due on this tax deadline.
Seattle startups can claim Research & Development Tax Credits on Form 941.
Delaware Quarterly Estimated Franchise Tax. Pay 40% of estimated annual amount (if annual amount expected to exceed $5,000).
Federal Quarterly Estimated Tax 2nd installment (second quarter 2024).
Seattle Q2 Business License Tax for Quarterly Filers
Washington Q2 State Fund Quarterly Report (Payroll Tax) due.
Washington Q2 Excise Tax Return due.
Claim Research & Development Tax Credits on Form 941 .
Delaware Quarterly Estimated Franchise Tax. Pay 20% of your estimated annual amount (if annual amount expected to exceed $5,000).
Federal Quarterly Estimated Tax 3rd installment (third quarter 2024).
C Corp Form 1120 Tax Return final due date for Seattle startups if extension was filed.
Washington Q3 Excise Tax Return due.
Seattle Q3 Business License Tax for Quarterly Filers.
Remaining 50% of Washington Personal Property Tax due.
Washington Q3 State Fund Quarterly Report (Payroll Tax) due.
Claim your Research & Development Tax Credits on Form 941.
Delaware Quarterly Estimated Franchise Tax, Pay 20% of estimated annual amount (if annual amount expected to exceed $5,000).
Federal Quarterly Estimated Tax 4th installment (fourth quarter 2024).
Renew your business license annually.
View tax compliance dates for Austin, Boston, New York City, Palo Alto, San Francisco, Santa Monica, Seattle, Washington DC, Atlanta, Salt Lake City, Mountain View, Chicago, Dallas, Miami, and San Jose
How Much Does a Startup Tax Return Cost? Try Kruze Consulting's Tax Preparation Pricing Tool.
How much can your startup save in payroll taxes? Estimate your R&D tax credit using our free calculator.
Every startup is different and so are its tax compliance needs. This is only a guideline. Please consult your tax professional. IRS Circular 230 Disclaimer: To ensure compliance with IRS Circular 230, any U.S. federal tax advice provided in this communication is not intended or written to be used, and it cannot be used by the recipient or any other taxpayer for the purpose of avoiding tax penalties that may be imposed on the recipient or any other taxpayer. Copyright © Kruze Consulting
Check our 2026 Tax Deadlines For C-Corp Startups or Click for your customized tax compliance calendar by startup hub
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Founder & CEO, Vanessa Kruze, is a CPA, Deloitte Tax alumni, and former Controller of a 120+ FTE startup. Our Staff Accountants and Controllers come from the Big 4 and venture backed startups.
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