The California-only calendar for 2026
Federal deadlines are covered in our full 2026 S corp calendar. Below is everything California adds on top.
Three quirks that trip up California S corp owners
1. The extension doesn't extend payment. California's automatic extension is generous — no form to file, six extra months — but it applies to the paperwork only. The 1.5% franchise tax balance is due March 16 regardless, and interest accrues from that date.
2. The $800 is due even in a loss year. The minimum franchise tax applies whether the corporation is active, inactive, or losing money. The only exception is a qualifying newly formed corporation's first taxable year.
3. Personal and corporate estimates run on different schedules. Your corporation pays four equal-quarter installments ending December 15. You personally pay on California's 30/40/0/30 weighting ending January 15. Two schedules, one owner — this is where most missed payments happen.
What missing a deadline costs
$18 per shareholder, per month — the FTB's late-filing penalty on Form 100S, for up to 12 months. On top of that: a delinquent penalty of 5% of unpaid tax per month (capped at 25%), plus interest. And the federal side is worse — $255 per shareholder per month for a late 1120-S.
Frequently asked questions
When is California Form 100S due in 2026?
March 16, 2026 for calendar-year S corps (March 15 is a Sunday). Filing auto-extends to September 15, 2026 with no form required, but payment is due March 16.
When is the $800 franchise tax due?
With your first Form 100-ES installment on April 15, 2026. Owed every year the corporation exists, waived only for a qualifying first year after formation.
What are the 2026 Form 100-ES due dates?
April 15, June 15, September 15, and December 15, 2026 — the 15th day of the 4th, 6th, 9th, and 12th months of the tax year.
Why no September personal estimate?
California weights Form 540-ES payments 30% (April), 40% (June), 0% (September), 30% (January). The Q3 installment is simply zero.
What's the penalty for a late Form 100S?
$18 per shareholder per month (up to 12 months), plus a delinquent-filing penalty of 5% of unpaid tax per month (up to 25%) and interest.
When is my Statement of Information due?
By the end of the calendar month in which your corporation originally registered with the Secretary of State — a different month for every corporation, which is exactly why it gets missed.