How to Complete and File California Form 100W: Water’s-Edge Filers

California Form 100W is the franchise or income tax return filed by a corporation (or unitary group) that has elected water’s-edge reporting under Revenue and Taxation Code Section 25110. You file it in place of Form 100, attach Form 100-WE and the supporting schedules your group’s situation calls for, apply the 8.84 percent corporate rate to income apportioned to California (never less than the $800 minimum franchise tax), and pay estimated tax across the year on California’s unequal 30/40/0/30 installment schedule. For a calendar-year filer, the return is due April 15.

Who Files Form 100W

Any unitary business group with a valid water’s-edge election files Form 100W rather than Form 100. The election limits the combined report to domestic entities and certain foreign affiliates with meaningful U.S. activity, instead of pulling every worldwide affiliate into the computation.¹

The group includes U.S.-incorporated corporations under more than 50 percent common control; any corporation (domestic or foreign) whose average U.S. property, payroll, and sales factors reach at least 20 percent; controlled foreign corporations with Subpart F income, included in proportion to that Subpart F income over total earnings and profits; DISCs, FSCs, and export trade corporations; and any other foreign corporation to the extent of its U.S.-located factors and income.² Foreign affiliates outside those categories stay out of the combined report, which is the point of making the election in the first place.

When Form 100W Is Due

Form 100W is due on the 15th day of the fourth month after the close of the taxable year. Calendar-year filers file by April 15, with the deadline rolling to the next business day when it falls on a weekend or holiday.³

California grants corporations an automatic six-month extension to file. No written request is required, but the corporation must actually file by the extended date and its powers and privileges cannot be suspended or forfeited as of the original due date.⁴ The extension covers filing only. Any balance owed is still due by the original deadline, and penalties and interest run from that date.

Estimated Tax Payments

Water’s-edge filers pay estimated tax quarterly, and California does not follow the federal pattern of four equal installments. The California split is 30 percent, 40 percent, zero, and 30 percent across the four quarters.⁵ For a calendar-year corporation in 2026:

April 15, 2026: 30 percent of estimated tax
June 15, 2026: 40 percent of estimated tax
September 15, 2026: no payment due
December 15, 2026: 30 percent of estimated tax

Fiscal-year filers use the same percentages on the 15th day of the fourth, sixth, ninth, and twelfth months of the taxable year. The third-quarter zero catches people off guard; do not treat the December installment as optional on the assumption it mirrors the federal calendar. Underpayment of any single installment carries its own penalty even when total payments for the year come out close to the right number, so project each installment against the current year’s expected liability rather than relying on prior-year tax, particularly if affiliates are entering or leaving the combined report.

Schedules and Attachments to Assemble

Most of the preparation time on Form 100W goes into attachments. Pull these together before you start the main return:

Form 100-WE, Water’s-Edge Election. Required on the first Form 100W, and a copy of the original election should be attached to every subsequent return filed during the election period.⁶
Schedule R, Apportionment and Allocation of Income. Computes the share of business income apportioned to California and allocates nonbusiness income under RTC Sections 25123 through 25127.⁷
Schedule R-7, Election to File a Unitary Taxpayers’ Group Return. Used when eligible members of the water’s-edge group file one combined return. Each participating member must be in the combined report for the entire year and share the key corporation’s taxable year and statutory filing date.⁸
Schedule H (100W), Dividend Income Deduction. Computes the deduction for qualifying dividends received from corporations whose average U.S. property, payroll, and sales factors are below 20 percent and whose voting stock is more than 50 percent owned by the water’s-edge group. The standard deduction is 75 percent; dividends from certain foreign construction projects qualify for 100 percent.⁹
Form FTB 2416, used when controlled foreign corporations are included in the combined report.
Form FTB 4197, Information on Tax Expenditure Items, reporting credits, deductions, and exemptions for FTB’s annual reporting under RTC Section 41.¹⁰

Completing the Return

Start with the identification block: legal name, mailing address, California corporation number, FEIN, California Secretary of State file number, and the beginning and ending dates of the taxable year. Indicate whether the income is included in a combined report and whether the group operates wholly within California or both within and outside the state.¹¹

Income and California Adjustments

Line 1 starts with net income or loss from the federal return before state adjustments. California then adds items like taxes on income deducted federally and non-California state income taxes, and subtracts items like interest on U.S. obligations and certain intercompany dividends. For water’s-edge filers, net income from included controlled foreign corporations flows in through Form FTB 2416, and the foreign dividend deduction from Schedule H (100W) is entered as a subtraction.¹¹

Net Operating Loss Deduction (Suspended for 2024–2026)

For taxable years 2024 through 2026, California has suspended the NOL deduction for most corporate taxpayers. Losses can still be computed and carried over during the suspension, and the carryover period is extended by one year for each suspension year.¹² The suspension does not apply if the corporation’s income subject to California taxation is under $1 million, and disaster loss carryovers are unaffected. If your group’s California income is $1 million or more, do not claim an NOL deduction on this return.

Apportionment

Schedule R splits business income between California and other jurisdictions, with the resulting percentage applied on the main return to produce the amount taxable in California. Nonbusiness income is allocated to specific states under RTC Sections 25123 through 25127.¹³ Misclassifying nonbusiness income as business income, or the reverse, is one of the more common audit triggers on water’s-edge returns.

Tax Rate and Minimum Franchise Tax

The corporate franchise tax rate is 8.84 percent, applied to net income after apportionment.¹⁴ The corporate alternative minimum tax rate is 6.65 percent; if AMT applies, the corporation owes whichever amount is greater. The minimum franchise tax of $800 applies regardless of income to every corporation incorporated, registered, or doing business in California.¹⁵

Credits and Prior-Year Overpayments

After computing the tax, apply eligible credits using the three-digit name code for each. Prior-year overpayments credited forward are entered separately.¹⁶ A corporation claiming the California Motion Picture and Television Production Credit (Program 4.0) attaches Form FTB 3541.¹⁰

Submitting the Return and Paying

Corporations that prepare the return using tax preparation software are required to e-file, which covers most filers in practice.¹⁷ For paper submissions, the mailing addresses differ only by zip code extension, so check it twice:¹⁰

With payment: Franchise Tax Board, PO Box 942857, Sacramento, CA 94257-0501
Without payment, or when payment is made electronically: Franchise Tax Board, PO Box 942857, Sacramento, CA 94257-0500
E-filed return with payment voucher (Form FTB 3586): Franchise Tax Board, PO Box 942857, Sacramento, CA 94257-0531

Payments can be made through FTB Web Pay directly from a checking or savings account at no charge.¹⁸ Electronic fund transfer, electronic funds withdrawal, and credit card are also accepted. Any balance owed is due by the original filing deadline, even if the group uses the automatic six-month extension to file.

Penalties for Late Filing or Late Payment

The late-payment penalty is 5 percent of the unpaid tax, plus 0.5 percent for every month or partial month the balance remains unpaid. The monthly portion caps at 40 months, and the total penalty cannot exceed 25 percent of the unpaid tax.¹⁹ Interest accrues on top of the penalty from the original due date. Estimated tax underpayments carry their own penalty, computed installment by installment, so a shortfall in any single quarter can trigger a charge even if full-year payments look adequate.

Keeping the Election in Effect

The water’s-edge election runs for 84 months (seven years) from the first day of the taxable year it takes effect.²⁰ For a valid election, the return must be computed consistently with water’s-edge treatment, filed on Form 100W (or Form 100S for S corporations), with Form 100-WE attached.⁶

When a corporation that was not previously subject to California tax joins a unitary group with an election in place and later becomes taxable here, it is generally deemed to have elected along with the rest of the group. When an electing and a non-electing taxpayer merge into a new unitary group, the non-electing side is deemed to have elected if the electing side has larger total business assets.²¹

Ending the election before 84 months have run requires FTB consent for good cause, defined the same way as Treasury Regulations Section 1.1502-75(c). After termination, whether at the end of the 84-month period or earlier with consent, the group cannot make a new water’s-edge election for any taxable year beginning within the following 84 months unless the FTB waives that waiting period for good cause.²¹

1
Franchise Tax Board. Instructions for Form 100W – Section: Introduction
2
Cornell Law Institute. California Code of Regulations 18 CCR 25110 – Water’s-Edge Group
3
Franchise Tax Board. Due Dates: Businesses
4
Franchise Tax Board. Payment for Automatic Extension for Corporations and Exempt Organizations
5
Franchise Tax Board. 2026 Instructions for Form 100-ES Corporation Estimated Tax
6
Legal Information Institute. 18 CCR 25113 – Water’s-Edge Election
7
Franchise Tax Board. California Schedule R – Apportionment and Allocation of Income
8
Franchise Tax Board. 2024 Schedule R Apportionment and Allocation of Income
9
Franchise Tax Board. 2023 Instructions for Schedule H (100W) Dividend Income Deduction
10
Franchise Tax Board. 2025 Instructions for Form 100W Corporation Tax Booklet – Water’s-Edge Filers
11
Franchise Tax Board. California Corporation Franchise or Income Tax Return – Water’s-Edge Filers
12
Franchise Tax Board. Net Operating Loss
13
Franchise Tax Board. 2024 Instructions for Schedule R Apportionment and Allocation of Income
14
Franchise Tax Board. Business Tax Rates
15
Franchise Tax Board. Corporations – Section: Minimum Franchise Tax
16
Franchise Tax Board. California Corporation Franchise or Income Tax Return – Water’s-Edge Filers
17
Franchise Tax Board. e-File for Business
18
Franchise Tax Board. Pay by Bank Account (Web Pay)
19
Franchise Tax Board. FTB Pub 1024 Penalty Reference Chart
20
Franchise Tax Board. 2024 Water’s-Edge Election – California Form 100-WE
21
California Legislative Information. California Code Revenue and Taxation Code RTC 25113