2027 California Tax Deadlines

Last updated: July 29, 2026

Key California tax dates at a glance

This block is the single date reference for 2027 California filing, payment, and extension planning.

• April 15, 2027: First California estimated tax payment under the 30% / 40% / 0% / 30% schedule.
• June 15, 2027: Second California estimated tax payment.
• September 15, 2027: Third California estimated tax payment, with 0% installment due under California's schedule.
• January 18, 2028: Fourth California estimated tax payment.
• March 15, 2028: California S Corporation and Partnership returns and payments due.
• April 18, 2028: California Individual and C Corporation returns and payments due.
• September 15, 2028: Extended California S Corporation and Partnership returns due, file only.
• October 16, 2028: Extended California Individual returns due, file only.
• November 15, 2028: Extended California C Corporation returns due, file only.

When are California taxes due in 2027?

California's 2027 calendar-year S Corporation and Partnership returns are generally due March 15, 2028, while Individual and C Corporation returns and payments are due April 18, 2028. Estimated payments and filing-only extensions should be tracked separately because California uses state-specific installment and extension rules.

When is the California C Corporation return due?

California C Corporations file and pay California corporate income tax by April 18, 2028. The approved 2027 draft uses Form 100 for the calendar-year C Corporation filing.

• Complete Form 100.
• File electronically through CalFile and FTB-approved e-file software or approved software where available.
• Pay by the original due date of April 18, 2028.
• Postmark any mailed return by the due date if paper filing is allowed.

What are the California C Corporation extension rules?

The extended California C Corporation filing deadline is November 15, 2028. The extension is to file only; payment remains due on April 18, 2028.

When are California S Corporation and Partnership returns due?

California S Corporations and Partnerships file their state pass-through returns by March 15, 2028. Payment also remains tied to the original California due date.

Which California pass-through forms are required?

• Form 100S: S Corporation Franchise or Income Tax Return.
• Form 565: Partnership Return of Income.
• Form 568: Limited Liability Company Return of Income where applicable.

What are the California pass-through extension rules?

The extended California S Corporation and Partnership filing deadline is September 15, 2028. The extension is to file only; payment remains due on March 15, 2028.

When is the California Individual income tax return due?

California Individuals file and pay their Individual income tax returns by April 18, 2028. The approved 2027 draft uses the California resident and nonresident forms listed below.

Which California Individual forms are commonly used?

• Form 540: California Resident Income Tax Return.
• Form 540NR: California Nonresident or Part-Year Resident Income Tax Return.
• Form 540X: Amended Individual Income Tax Return.

What are the California Individual extension rules?

The extended California Individual filing deadline is October 16, 2028. The extension is to file only; payment remains due on April 18, 2028.

When are California estimated tax payments due?

California estimated payments generally apply when expected California tax after withholding and credits is $500 or more, or $250 if married/RDP filing separately.

• April 15, 2027: First California estimated tax payment under the 30% / 40% / 0% / 30% schedule.
• June 15, 2027: Second California estimated tax payment.
• September 15, 2027: Third California estimated tax payment, with 0% installment due under California's schedule.
• January 18, 2028: Fourth California estimated tax payment.

What California rules should tax professionals watch in 2027?

Beyond the core deadline calendar, California has several filing and payment mechanics that should stay on the review checklist:

How does California's automatic extension work?

California generally grants automatic extensions to file, but payment remains due on the original due date. For calendar-year 2027, Individual and C Corporation payments remain due April 18, 2028.

What is unusual about California estimated payments?

California uses a 30% / 40% / 0% / 30% installment pattern, so the September 15, 2027 estimate date carries a 0% installment under the approved draft.

What California LLC rules should teams watch?

California LLCs generally face an $800 annual tax, plus a graduated LLC fee when California-source income exceeds $250,000. Confirm entity classification and return schedule before assuming the Partnership pattern applies.

Tax-professional context: Several key considerations make California's tax landscape particularly complex for 2027. California has some of the highest state income tax rates in the nation, extensive compliance requirements, and unique provisions that differ significantly from federal tax law.

Electronic filing requirements:

• C Corporations and pass-through entities must file electronically in most cases.
• Individuals can use CalFile for free electronic filing.
• Professional preparers must use approved software vendors.
• Large taxpayers have mandatory e-file requirements.

LLC Annual Tax and Fee Requirements:

• LLCs owe an annual tax of at least $800.
• The LLC fee is based on total income from California sources.
• A graduated fee applies to LLCs with California-source income over $250,000.
• Due dates vary but generally follow Partnership return schedules.

Highest marginal income tax rates in the United States: California's progressive tax structure ranges from 1% to 12.3%, plus an additional 1% Mental Health Services Tax on high earners (effective top 13.3%).

Alternative Minimum Tax with different rules from the federal AMT: California maintains its own AMT system with regulations that differ from federal Alternative Minimum Tax calculations.

Mental Health Services Tax of 1% on income over $1 million: High-income taxpayers face an additional 1% tax on income exceeding $1 million to fund mental health services.

California conformity and non-conformity issues:

• California uses different depreciation rules and schedules.
• Certain business expenses receive different treatment.
• Retirement account distribution rules may differ.
• California has unique tax credits and deductions.
• California does not conform to many recent federal tax law changes.

High-income taxpayer considerations:

• Bunching strategies for deductions and income.
• Multi-state tax planning for residents with income in other states.
• Estimated tax planning to avoid underpayment penalties.
• Alternative Minimum Tax planning and compliance.

Which sources were used for this California deadline guide?

The sources below are placed above the CTA so Webflow editors and reviewers can verify the deadline logic before publishing.

• California FTB personal due dates.
• California FTB business due dates.
• California FTB CalFile.
• California FTB 2025 Form 540 booklet.

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