2026 Tax Deadlines for San Diego Startups

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.