2026 Tax Deadlines for San Diego Startups
In 2026, San Diego-based companies should plan for the April 15 federal and California corporate return deadlines, as well as the April 1 business property statement filing handled through the county assessor.
Upcoming San Diego deadlines in 2026
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 2026).
Total 26 tax events for San Diego in 2026
Click the links to learn more about these filings and 2026 San Diego startup tax deadlines
Federal Quarterly Estimated Tax 4th installment (fourth quarter 2025).
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.
San Diego 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 San Diego startup will pay a minimum of $400, which increases if you have significant funding.
For San Diego 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).
San Diego County: Business Property Statement (Form 571-L) due.
California corporation franchise or income tax return (Form 100) due.
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 San Diego 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 San Diego startup employees to make contributions to Individual Retirement Accounts (IRAs) for 2025 (Employee Benefits).
San Diego startups can claim Research & Development Tax Credits on Form 941.
San Diego County: 571-L penalty date / late filing trigger.
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).
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 San Diego startups if extension was filed.
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 2026).
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City of San Diego: Business tax certificate renewal. Typically renewed annually based on the business start/anniversary cycle.
Federal Quarterly Estimated Tax 4th installment (fourth quarter 2025).
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.
San Diego 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 San Diego startup will pay a minimum of $400, which increases if you have significant funding.
For San Diego 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).
San Diego County: Business Property Statement (Form 571-L) due.
California corporation franchise or income tax return (Form 100) due.
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 San Diego 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 San Diego startup employees to make contributions to Individual Retirement Accounts (IRAs) for 2025 (Employee Benefits).
San Diego startups can claim Research & Development Tax Credits on Form 941.
San Diego County: 571-L penalty date / late filing trigger.
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).
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 San Diego startups if extension was filed.
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 2026).
City of San Diego: Business tax certificate renewal. Typically renewed annually based on the business start/anniversary cycle.
SAN DIEGO, STARTUPS AND TAXES
San Diego remains one of California’s most important startup markets in 2026, with particular strength in biotech, life sciences, healthtech, defense, telecom, and software. The region benefits from a deep research base tied to UC San Diego and major scientific institutions, giving founders access to specialized talent and a strong commercialization pipeline.
Compared with San Francisco, San Diego offers a somewhat more distributed and sector-specialized ecosystem, but it remains highly attractive for venture-backed companies that need engineering or life sciences talent plus access to Southern California customers, operators, and investors. Its mix of research institutions, defense-adjacent innovation, and scaling software companies makes it one of the more durable startup hubs in the state.
Key taxing authorities for San Diego-based businesses in 2026 are:
Total 21 tax events for San Diego in 2025
Click the links to learn more about these filings and 2025 San Diego startup tax deadlines
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.
San Diego 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.
For San Diego 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.
Delaware Annual Franchise Report filing deadline. Your San Diego 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.
IRS ACA Compliance 1094-B, 1095-B, 1094-C, and 1095-C filings are due (e-file).
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 San Diego 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 San Diego startup employees to make contributions to Individual Retirement Accounts (IRAs) for 2023 (Employee Benefits).
San Diego 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).
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 San Diego startups if extension was filed.
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).
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.
San Diego 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 San Diego 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.
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 San Diego 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 San Diego startup employees to make contributions to Individual Retirement Accounts (IRAs) for 2023 (Employee Benefits).
San Diego 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).
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 San Diego startups if extension was filed.
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).
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
Navigating Local Tax Requirements
Local & City-Specific Startup Tax Deadlines
Find important local and city-specific startup tax deadlines here, including state and municipal filing dates, estimated payment deadlines, and key compliance requirements for major business hubs.