How are receipts from services performed at sea sourced for state tax purposes?
Edvin Givargis Published 6 minute read
The short answer
By a method the taxpayer builds, because no rule reaches the water. California sources service receipts to where the customer receives the benefit of the service, applied through a cascade that starts with the taxpayer's books and moves to reasonable approximation when the books do not answer (Cal. Code Regs., tit. 18, section 25136-2). For dredging, towing, salvage, and marine construction, the books rarely answer, there is no ocean-specific rule in the regulation, and the cascade lands almost immediately on reasonable approximation, which means the real question is what approximation is reasonable for work performed on the water. The defensible architecture has two parts. First, a proxy for locating the work: port days, the number of days a vessel spends in each jurisdiction's ports and waters, a metric the state itself blesses in adjacent contexts, from the commercial fishing regulation to the Franchise Tax Board's own audit manual treatment of barge operations. Second, a map of the water: California's own waters run three miles from the coastline, United States territorial waters continue to roughly twelve nautical miles, about 13.8 statute miles, and beyond that lies international water, where a benefit-received analysis supports sourcing the receipts to no state at all. Built together, the port-day proxy and the water-line map produce a hybrid method: near-shore work sourced by port days, work beyond the territorial limit treated as non-U.S. receipts, and the band between the state line and the territorial limit handled deliberately, because it is the one zone where the authorities genuinely run out. Whatever method emerges, its defense is consistency and documentation, not citation, and that changes how the file should be built.
Why the cascade runs out, and where the proxy comes from
The market-based rules assign a service receipt to California to the extent the customer receives the benefit here, and for a business customer the regulation works through a sequence: the contract and books and records first, reasonable approximation when those do not fix the location. A dredging contract fixes the project site; a towing engagement fixes two endpoints and a route; a salvage job fixes a position at sea. None of these translates automatically into a percentage of the receipt earned in California, and the regulation offers no marine rule to do the translation. What California does offer is analogy. The special industry regulation for commercial fishing (Cal. Code Regs., tit. 18, section 25137-5) apportions that industry using port days, on the theory that where a vessel touches is the workable measure of where its economic activity happens, and the Board's audit manual applies port-day thinking to barge operations while reserving voyage-day methods for long-haul sea transportation. True carriers, vessels in the business of transporting freight or passengers for hire on defined routes, may fall within a special formula of their own, and where a special regulation actually applies, it governs. For the marine service business that fits no special rule, the analogies do a different job: they establish that a day-count, location-touch proxy is a method the state itself considers reasonable, which is most of the battle when the standard is reasonable approximation. Port and voyage logs are records the operator already keeps, contemporaneous, third-party corroborated through harbor records and charters, and vessel-specific, which makes the proxy cheap to run and hard to impeach.
The water lines, and the hybrid method
The map matters because sourcing by port days alone quietly assumes every working day belongs to some state, and for ocean work that assumption is wrong. Three lines divide the water. Out to three miles from the coast, the water is California (or the neighboring coastal state) and days there are that state's days. From three miles to the territorial limit, roughly twelve nautical miles, the water is the United States but no state, a band the sourcing rules simply do not address: the benefit-received analysis has no state to point to, yet the receipts are not foreign either, and positions taken for this band should be chosen consciously and held consistently, because it is the zone an auditor can argue in either direction. Beyond the territorial limit, the work is performed outside the United States, and the supportable position is that the benefit of the service is received outside any state, so the receipts source nowhere for state formula purposes, reducing every state's numerator while remaining in the denominator. The hybrid method assembles these pieces: identify each engagement's receipts, allocate the engagement's working days among the zones using the logs, source the state-water days by state, treat the beyond-the-limit days as non-U.S., and decide the middle band once, in writing. For a fleet whose big revenue streams differ in kind, the method should be run stream by stream: harbor and bay work is nearly all state water and sources almost entirely to the project state, long tows are mostly open ocean and source almost nowhere, and the documentation for each is different, project records for the first, voyage logs and route plots for the second.
Two era notes keep the California method current. The regulation this analysis runs on was substantially amended effective for taxable years beginning on or after January 1, 2026, restructuring the cascade and the burden framework, including when the Board may displace a taxpayer's approximation; the two-era mechanics are covered in the companion article on market-based sourcing of services and intangibles, and an at-sea method built before the amendment should be re-papered against the new rules rather than assumed forward. And Washington, the other state a Pacific fleet meets first, runs a parallel benefit-received cascade for its business and occupation tax that opens with a reasonable and consistent method of attribution, so a single well-documented port-day method can, and should, be applied consistently on both sides of the state line, with the B&O return and the California return telling the same story about the same days.
Practice notes
The method memo is the deliverable, and it should exist before the first return takes a position: the proxy chosen, the analogies relied on, the water-line treatment including the middle band, the records that feed the computation, and the commitment to consistency across states and years. Once adopted, the method is an asset precisely because approximation methods are judged on reasonableness and consistency; a taxpayer that changes proxies year to year to chase the lowest number has forfeited the presumption of good faith that a standing method earns. Operationally, the log discipline is everything: vessel-by-vessel day counts by jurisdiction, kept as the year runs, tied to charters and harbor records, because the reconstruction alternative is expensive and unpersuasive. Watch the interaction with the rest of the return: the same day counts that source receipts also inform property factor situs for mobile hulls and payroll assignments for the crews aboard them, and the three factors should not tell three different stories about where a vessel spent the year. And treat the special regulations as a boundary question worth revisiting as the business mixes: an operator that grows a scheduled freight route may drift into a true transportation formula for that stream, while the project work stays on the approximation method, and running each stream under the rule that actually governs it is both the correct answer and the audit-resistant one.
This article states the law as of September 15, 2026
Statutes, rates, thresholds, and agency practice change, and a different set of facts can change the answer. Before acting on anything discussed above, contact G&G State Tax Group to confirm what has changed since this was written and how the rules apply to a specific situation.
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