California estimates: 30/40/0/30
California front-loads its estimated tax: 70% of the year's tax is due by mid-June and nothing is due in September. Founders who pay equal federal-style quarters underpay California in the spring and get a penalty notice for it.
| Installment | Share | Corporations (calendar year) | Individuals |
| 1st | 30% | April 15 | April 15 |
| 2nd | 40% | June 15 | June 15 |
| 3rd | 0% | September 15 | September 15 |
| 4th | 30% | December 15 | January 15 (next year) |
Fiscal-year corporations use the 15th day of the 4th, 6th, 9th, and 12th months of their tax year. Dates falling on a weekend or holiday move to the next business day.
Corporations: C-corps and S-corps
A corporation estimates its California tax for the year (8.84% of apportioned net income for a C-corp, 1.5% for an S-corp) and pays it in the four installments above using Form 100-ES or Web Pay. The first installment must be at least the $800 minimum franchise tax, even if the year's total tax will turn out to be exactly $800. A new corporation in its first taxable year is exempt from the $800 minimum, but still owes estimates on any income tax it expects (see the 8.84% guide).
Safe harbor: a corporation avoids the underpayment penalty if each installment covers its share of the lesser of 100% of this year's tax or 100% of last year's tax. Large corporations, California taxable income of $1 million or more in any of the three prior years, can use last year's tax only for the first installment.
Individuals, including LLC and S-corp owners
Owners of pass-through businesses pay California tax on their share of profit through their own estimates (Form 540-ES), on the same 30/40/0/30 pattern with the final installment in January. The safe harbor is the lesser of 90% of this year's tax or 100% of last year's: 110% if last year's AGI exceeded $150,000 ($75,000 married filing separately). Taxpayers with AGI of $1 million or more cannot use the prior-year safe harbor at all.
LLCs pay a separate layer
An LLC's own obligations don't follow the 30/40/0/30 pattern:
- $800 annual tax: due in full by the 15th day of the 4th month (April 15 for calendar-year LLCs) on Form 3522.
- § 17942 gross-receipts fee: estimated and paid by the 15th day of the 6th month (June 15) on Form 3536. Underpaying triggers a 10% penalty unless you paid at least last year's fee (walkthrough).
These penalties stack independently of your personal estimates. An owner can be fully paid up on Form 540-ES and still owe the LLC a fee penalty.
The PTE elective tax adds a June payment
Partnerships, LLCs taxed as partnerships, and S-corps that elect California's pass-through entity tax (9.3% of qualified net income, extended through 2030 by SB 132) owe a June 15 prepayment of the greater of $1,000 or 50% of the prior year's PTE tax. From 2026, missing or underpaying that June payment no longer voids the election: instead the owners' credit is reduced by 12.5% of the shortfall. The balance is due with the entity's return.
Worked example: C-corp expecting $400,000 of profit
Expected tax: 8.84% × $400,000 = $35,360. Installments: $10,608 on April 15, $14,144 on June 15, $0 on September 15, and $10,608 on December 15. A company that paid $8,840 each quarter instead would be about $16,000 short by June 15 and owe underpayment interest on that gap until December.