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S Corporation Extensions & Payments for California S Corps

IRS Form 1120-S + California Form 100S (Deadlines, Extensions, and What You Actually Pay)

If your S corporation is based in California, you’re dealing with two parallel compliance tracks every year:

• Federal: IRS Form 1120-S + shareholder K-1s
• California: Form 100S + California S-corp tax/estimated payments

Key rule: an extension usually extends the time to file, not the time to pay.

Key due dates (calendar-year S corporation)

For most S corporations with a tax year ending 12/31:

Federal (IRS Form 1120-S)

• Return due: 15th day of the 3rd month after year end (typically March 15; if weekend/holiday, next business day)
• Extension: File Form 7004 by the original due date for an automatic 6-month extension (typically to September 15; weekend/holiday shifts apply)
• Payment: Form 7004 does not extend time to pay any federal tax due (rare for S corps, but possible in specific situations)

California (CA Form 100S)

• Return due: generally 15th day of the 3rd month after year end (typically March 15; weekend/holiday shifts apply)
• Filing extension: California generally allows an automatic 6-month filing extension for Form 100S (no extension form required to extend the filing deadline)
• Payment: the automatic filing extension does not extend time to pay—California expects the full tax due to be paid by the original due date (commonly paid with FTB 3539, Payment for Automatic Extension)

Example (Tax Year 2025, calendar year S corp)

Because March 15, 2026 is a Sunday, the deadlines shift:

• Federal 1120-S due: March 16, 2026
• Federal extended due (Form 7004): September 15, 2026
• CA 100S due: March 16, 2026
• CA extended due: September 15, 2026

What payments are actually due for a California S corporation?

1) California S-corp entity-level tax (the big one)

California S corporations generally owe an entity-level tax that is commonly described as:

• 1.5% of net income, with an $800 minimum franchise tax, subject to exceptions and special situations

Practical takeaway:

• Even if you extend the return, you generally must pay what you owe by the original due date.
• Many CA S corps should plan for at least the $800 minimum, plus any additional tax based on California net income.

Important nuance (first-year planning): California has special rules for new entities (e.g., the first-year minimum tax waiver rules). Don’t blanket-assume the $800 always applies in year one—verify facts for newly formed/qualified corporations.

How to pay with the extension (if you owe):

• Use FTB Form 3539 to submit an extension payment by the original due date.

2) California estimated tax payments (when applicable)

If your S corporation expects to owe California tax for the year, California may require estimated tax installments. The standard corporate schedule is:

• 15th day of the 4th month
• 15th day of the 6th month
• 15th day of the 9th month
• 15th day of the 12th month of the tax year

For a calendar-year taxpayer, that’s typically:

• April 15, June 15, September 15, December 15

(These are typically made using California corporate estimated tax payment instructions/vouchers, as applicable.)

3) Federal payments: usually “none,” but don’t assume

Most S corporations don’t pay federal income tax at the entity level because income flows through to shareholders on K-1s.

However, entity-level federal taxes can apply in certain circumstances (common examples include built-in gains tax and certain passive income taxes). If the S corp owes federal tax:

• The extension extends filing, not payment.

Do you have to “file an extension” for California Form 100S?

Usually no—California generally provides an automatic filing extension for 100S.

But here’s the catch:

• If you owe tax, you generally should pay by the original due date (commonly via FTB 3539).
• If you don’t owe, you typically just file by the extended due date—but still confirm you’re not missing a minimum tax, estimate requirement, or special tax situation.

Practical compliance checklist (California S corp)

By the original due date (typically mid-March for calendar-year)

• File IRS Form 7004 if you need a federal extension
• Pay any federal tax due (if applicable)
• Pay California tax due by the original due date
• If paying CA with the extension, submit payment via FTB 3539

By the extended due date (typically mid-September for calendar-year)

• File IRS Form 1120-S
• Deliver K-1s to shareholders
• File CA Form 100S

 

FAQs

Does the extension extend the time to pay California’s S-corp tax?

No. California’s extension is primarily an extension to file, not to pay. If you owe, the expectation is that the full tax is paid by the original due date.

Does IRS Form 7004 extend the time to pay federal tax?

No. Form 7004 extends the time to file, not the time to pay any tax due.

What are California corporate estimated tax due dates?

Generally: the 15th day of the 4th, 6th, 9th, and 12th month of the tax year.

 

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