California estimated tax payments for corporations follow an uneven 30%/40%/0%/30% installment schedule and require every corporation doing business in the state to prepay 100% of its current-year tax liability, including the $800 minimum franchise tax. The rules apply to C corporations, S corporations, and LLCs taxed as corporations, and they differ enough from the federal system that assuming the two match is one of the fastest ways to trigger a penalty.
Who Owes Estimated Tax and How Much
Every corporation doing business in California owes the $800 annual minimum franchise tax whether or not it earns any income.1Franchise Tax Board. Corporations Above that floor, tax is projected net income multiplied by the applicable rate: 8.84% for C corporations,2Franchise Tax Board. C Corporations and 1.5% for S corporations.3Franchise Tax Board. S Corporations
The estimated payments must cover 100% of current-year tax. For this purpose, “tax” is broader than regular income tax. It includes alternative minimum tax, S corporation taxes from Schedule D, excess net passive income, QSub annual tax, credit recapture, and the minimum franchise tax itself.4Franchise Tax Board. 2025 Instructions for Form 100-ES Corporation Estimated Tax
The First-Year Break
Corporations incorporated or qualified in California on or after January 1, 2020, do not owe the $800 minimum franchise tax in their first taxable year.1Franchise Tax Board. Corporations Net income earned that first year is still taxed at the regular rate, so estimated payments can still be required if projected income is high enough. The exemption also creates a common year-two surprise: the full $800 kicks in and must be paid with the first installment.
The Installment Schedule
California does not split the year into four equal quarters. Payments follow a lopsided allocation, and the third installment is zero:4Franchise Tax Board. 2025 Instructions for Form 100-ES Corporation Estimated Tax
- First installment, 30%, due the 15th day of the 4th month of the tax year
- Second installment, 40%, due the 15th day of the 6th month
- Third installment, 0%, no payment required
- Fourth installment, 30%, due the 15th day of the 12th month
For calendar-year corporations, those dates are April 15, June 15, September 15 (nothing due), and December 15. Fiscal-year corporations shift the months to match their own year. A due date that lands on a weekend or legal holiday moves to the next business day.5Franchise Tax Board. California Form 100-ES Corporation Estimated Tax
The entire $800 minimum franchise tax rides with the first installment, even when total projected liability is only the minimum. A corporation expecting to owe $10,000 for the year pays $3,000 first (30%), and that $3,000 includes the $800. Corporations with QSub annual tax add it to the first installment too.4Franchise Tax Board. 2025 Instructions for Form 100-ES Corporation Estimated Tax
The Large Corporation Rule
The FTB defines a “large corporation” as one that had California net income of $1 million or more in any of the three taxable years preceding the current year, calculated without regard to net operating loss deductions.6Franchise Tax Board. 2024 Instructions for Form 100-ES Corporation Estimated Tax
Large corporations cannot rely on last year’s tax to size the first installment. They must estimate current-year liability and pay 30% of that estimate by the first due date. A large corporation that leans on the prior-year safe harbor for installment one anyway sees the shortfall added to installment two.6Franchise Tax Board. 2024 Instructions for Form 100-ES Corporation Estimated Tax Corporations that did not reach $1 million in any of the three preceding years can use the prior-year safe harbor across all installments.
When Electronic Payment Is Mandatory
Two triggers push a corporation into required electronic payment. Total tax liability above $80,000 in any prior year is one. A single estimated tax payment or extension payment above $20,000 is the other, even if total liability stays below $80,000.7Franchise Tax Board. S Corporation Pass-Through Entity Elective Tax and Mandatory E-Pay Requirement Once either threshold is crossed, the mandate applies to every future payment and does not reset year to year.
The FTB accepts Web Pay (a direct bank debit through the FTB’s site, no charge), ACH debit initiated by the FTB, and ACH credit initiated by the corporation’s own bank.8Franchise Tax Board. Electronic Funds Transfer for Corporations Both ACH methods need at least one business day of lead time. Corporations required to pay electronically that send a paper check face a penalty on the amount paid.
What Happens When You Underpay
The FTB assesses an underpayment penalty automatically, calculated as an interest charge on the underpaid amount for the days it remained unpaid. For the period from July 2025 through June 2026, the corporate underpayment rate is 7%.9Franchise Tax Board. Interest and Estimate Penalty Rates Each shortfall installment is penalized separately based on the days it stayed unpaid relative to the days in the tax year.10California Franchise Tax Board. 2025 Form 5806 Underpayment of Estimated Tax by Corporations
Any installment that misses its required percentage (30%, 40%, or 30%) draws the penalty. The FTB uses Form 5806 to compute it, and corporations should complete the form with their annual return to see whether anything additional is owed.11Franchise Tax Board. 2024 Instructions for Form FTB 5806 Underpayment of Estimated Tax by Corporations
Safe Harbors That Prevent the Penalty
Two main safe harbors let a corporation avoid the underpayment penalty even when estimated payments don’t line up with actual tax.
Prior-Year Tax
Estimated payments equal to or above 100% of the prior year’s tax, prorated across the installments, avoid the penalty. The prior return must have covered a full 12-month period and shown a tax liability.6Franchise Tax Board. 2024 Instructions for Form 100-ES Corporation Estimated Tax Large corporations can only use this exception for the first installment, and any resulting reduction is added back to the second installment.
Annualized and Seasonal Income
For corporations that don’t earn income evenly, the FTB allows a standard annualization method and a separate seasonal variation. Annualization projects income through each installment period over a full year to compute what the tax would be. If a corporation’s payment meets or exceeds 100% of that annualized figure for the period, the installment is safe from penalty.4Franchise Tax Board. 2025 Instructions for Form 100-ES Corporation Estimated Tax
Waivers When the Penalty Still Applies
Even when the penalty technically applies, the FTB will not impose it to the extent the underpayment resulted from a new law enacted during the same taxable year. Legislation that changed the tax calculation after estimated payments were made can excuse the attributable portion of the penalty.12California Legislative Information. California Revenue and Taxation Code RTC 19142
Beyond that statutory carve-out, the FTB may waive penalties for reasonable cause. To request a waiver, complete Form 5806 showing the full penalty, write “Waiver” at the top, attach an explanation, and file it with the return.11Franchise Tax Board. 2024 Instructions for Form FTB 5806 Underpayment of Estimated Tax by Corporations A one-time penalty abatement is also available through FTB Form 2918 or by calling the FTB.13Franchise Tax Board. Help With Penalties and Fees Simply miscalculating tax owed is unlikely to qualify as reasonable cause.
Reconciling on the Annual Return
C corporations file Form 100 and S corporations file Form 100S, both due the 15th day of the 4th month after the tax year ends, which is April 15 for calendar-year filers. An automatic extension pushes the filing deadline to the 15th day of the 11th month, but estimated payments stay on their original schedule regardless of a filing extension.
When estimated payments exceed actual tax, the overpayment is refunded or credited to next year’s estimated tax. When they fall short, the balance is due with the return, and any Form 5806 penalty is reported there as well. Filing an extension does not pause the penalty clock. Each installment continues to accrue penalty from its own due date until paid, which is why the year’s estimates matter more than the return’s timing.
How California Differs From Federal Estimated Tax
Corporations manage both state and federal estimated payments, and the two systems diverge in ways that regularly trip up experienced tax teams.
Federally, a corporation owes estimated tax whenever it expects to owe $500 or more for the year.14Internal Revenue Service. Estimated Taxes California has no equivalent dollar threshold, since the $800 minimum franchise tax alone puts virtually every active corporation into the estimated payment system. Federal installments split into four equal 25% payments due on the 15th of the 4th, 6th, 9th, and 12th months.15Internal Revenue Service. Publication 509 (2026), Tax Calendars California’s 30%/40%/0%/30% split is unusual, and assuming the state matches the federal schedule is a common source of missed installments.
Federal underpayment rates also differ. For the first quarter of 2026, the IRS charges 7% on regular corporate underpayments and 9% on large corporate underpayments.16Internal Revenue Service. Quarterly Interest Rates California’s corporate underpayment rate for the same period is 7%, but because installment percentages and penalty calculation methods differ, the total exposure is not directly comparable. Running both calculations side by side each quarter is the reliable way to avoid surprises at filing.