Demurrage vs detention looks like a vocabulary question until the invoice arrives. Then it is a money question, and the answer depends on where the container stood when each day was counted.
Maersk’s explainer gives a clear split for imports. Demurrage is the time a full container spends inside the terminal, measured from offload from the vessel or train until it is picked up and gated out. Detention is the time it spends outside the terminal, from gate-out until the box is returned empty to the port or a depot. Export boxes run the other way: Mirage Metrics describes detention there as the stretch from empty pickup to full gate-in. Free time is the allowance a carrier gives for either clock before charges start. Demurrage and detention charges are incurred once you go beyond it, and Maersk says free time differs between ports and carriers.
GetTransport, which matches cargo with carriers, adds a number with a caveat. In its July 2026 guide, demurrage and detention free time at major US gateways is commonly 3 to 5 days, but there is no single national standard. Check the tariff or contract for each move.
The words are not used the same way everywhere
Mirage Metrics, which sells a freight invoice audit workflow, notes that carriers and regions use these terms differently. “Per diem” is a name used mainly in the United States for charges on equipment use, often what others call detention. Some tariffs grant a single combined free period that covers both clocks.
The US regulation fixes the vocabulary for its own purposes. Under 46 CFR 541.3, “demurrage or detention” covers any charges, per diem included, that a carrier, terminal or NVOCC assesses for the use of terminal space or shipping containers. Freight charges are excluded.
What a US invoice has to show
The Federal Maritime Commission’s billing rule, in force since May 2024, covers invoices from ocean carriers, marine terminal operators and NVOCCs. In February 2024 the FMC said most of the rule would take effect on 28 May 2024, with the invoice-contents section, 541.6, to follow once the Office of Management and Budget approved it. Section 541.6 lists the minimum content. Among other items: bill of lading and container numbers, the basis for billing you, invoice and due dates, free time in days with its start and end dates, the container availability date for imports, the specific dates charged, the total, the tariff rule or contract section behind the daily rate, a dispute contact and two certifications from the billing party. One certification says the billing party’s own performance did not cause or contribute to the charge.
Section 541.5 sets the consequence. Leave out any required item and the billed party has no obligation to pay that charge.
Mirage Metrics calls the availability date the one most often argued, and for US imports it must appear on the invoice. Three 30-day periods apply. The billing party must invoice within 30 calendar days of the date the charge was last incurred (an NVOCC has 30 days from the invoice it received). The billed party gets at least 30 calendar days from the invoice date to ask for mitigation, refund or waiver. The billing party must then attempt to resolve a request within 30 days of receiving it, or later if both sides agree.
The provision most guides quote, and what the court did to it
The original rule also limited who could be billed: the contracting party or the consignee, never both. The FMC’s February 2024 announcement called it a key provision.
On 23 September 2025 the D.C. Circuit held in World Shipping Council v. FMC that section 541.4 was arbitrary and capricious. The Commission had not explained its contractual-privity rationale against its blanket bar on billing motor carriers who were in privity. The court set the section aside, and an FMC final rule removed it from the CFR effective 29 December 2025. The FMC states that the other provisions of the rule remain in effect.
CargoLinked checked the regulations in August 2026 and found no FMC rule currently says who may be invoiced, and no replacement proposed. It adds that much published guidance still describes the old limit as current law. One requirement CargoLinked highlights as still standing is that the invoice must state why the billed party is the proper party liable. The FMC rule applies to US ocean trades. Mirage Metrics says that elsewhere the bill of lading, the tariff, the contract and local law govern.
A worked example, with invented numbers
Mirage Metrics walks through a fictional 40-foot import box. The contract starts demurrage free time the day after availability. The carrier’s invoice started it at discharge, so it billed four demurrage days where the terms support three. Mirage labels its figures as invented.
Invoice check, step by step
- Identify the clock: demurrage inside the terminal, detention outside it.
- Find the free time in your tariff or contract and when it starts (discharge, availability or the day after).
- On US trades, check every item 46 CFR 541.6 requires, including the availability date and the tariff rule behind the daily rate.
- Check the invoice date against the 30-day billing window.
- Dispute within 30 days of the invoice date if the dates do not match your container events.
Where Navo comes in on demurrage vs detention
My view: a status is only useful if you can see what it is made of. The dates in a demurrage claim are container events: discharge, availability, gate-out, return. If you cannot see where a date came from, you end up arguing from the carrier’s version.
Navo’s TrackingMCP covers containers across 229 carriers, normalised to one standard, with event freshness of 0 to 5 minutes cross-checked across 2 to 3 sources. It works from a dashboard, a REST API, webhooks or an MCP server, and Navo’s tools share the same events. We wrote about the two clocks for one carrier in our explainer on MSC free time. Our demurrage and detention page shows how those container dates feed a free time watch. If you want an agent working on the same events, you can request one at navo24.com/nav/.
Frequently asked questions
Is demurrage the same as detention?
In common usage they are two charges for two places. Demurrage covers a full container inside the terminal, from discharge until gate-out. Detention covers the time outside the terminal, until the empty box is returned. Some tariffs combine free time, and in the United States detention is often called per diem, so check your tariff.
Who pays demurrage and detention on US trades?
The party named on the invoice. Since the D.C. Circuit set aside section 541.4 in 2025, CargoLinked reports that no FMC rule limits who may be billed. The invoice must still state why the billed party is liable, and a missing required item removes the obligation to pay that charge under 541.5.
How long does a carrier have to send a demurrage and detention invoice?
Under 46 CFR 541.7, the billing party has 30 calendar days from the date the charge was last incurred, on US trades. An NVOCC has 30 days from the invoice it received. If the deadline is missed, the billed party is not required to pay the charge.
What if a demurrage invoice is missing information?
Under 46 CFR 541.5, leaving out any item required by section 541.6 means the billed party has no obligation to pay that charge. Check invoice contents and dates, including free time start and end and the container availability date, before checking the arithmetic.