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Demurrage and detention are the two charges that turn a well priced shipment into an expensive one, and the two most confused. They are different clocks, run by different parties, for different reasons. In the United States the Federal Maritime Commission regulates both, and the invoice rules in 46 CFR Part 541 decide whether a charge is payable at all.
The distinction
Demurrage is charged for cargo that stays inside the terminal beyond the agreed free time. You are paying the terminal, through the carrier, for occupying yard space.
Detention is charged for the carrier's container being kept outside the terminal beyond the free time. You are paying for the equipment, not the space.
On an import, demurrage runs from discharge until you collect the container; detention runs from collection until you return the empty. On an export, the sequence reverses: detention runs while you have the empty for loading, and demurrage applies if the loaded box sits at the terminal past its window.
| Charge | Where the box is | Whose asset |
|---|---|---|
| Demurrage | Inside the terminal | Terminal space |
| Detention | Outside the terminal | Carrier's container |
| Storage | Warehouse or CFS | Warehouse operator |
Some ports and carriers merge the two into a combined charge, called merged demurrage and detention. The FMC definition in 46 CFR 541.3 covers any charges, including "per diem" charges, related to the use of marine terminal space or shipping containers, excluding freight charges. Read the tariff rule, not the label.
How free time is counted
Free time is agreed at booking and expressed in days. Two details decide whether you use it well:
- Are the days calendar or working days? Weekends and public holidays consume calendar free time.
- When does the clock start? On discharge or on availability notification, as the tariff states, and not on the day you were told the vessel arrived.
Rates escalate by tier. The first days carry the lowest daily rate and each following tier costs more. Charges compound per container per day, so a delay on a five container shipment is billed five times each day.
An invoice must state the allowed free time in days, the start and end date of free time, the container availability date for imports, the earliest return date for exports, and the specific dates charged (46 CFR 541.6(b)). If you hold the dates, you can recompute the invoice.
What actually causes the charges
Customs holds, incomplete documentation, missing ISF, and manifest descriptions that trigger examination. Missing the release because the invoice was unpaid. No truck booked. A warehouse with no dock slot. Chassis shortages at the destination port. None of these is a freight problem, which is why none appears in a freight budget.
Filing discipline prevents most of them. Our notes on ISF filing requirements and AMS filing cover the two filings that hold a container, and AMS vs ISF sets out who owns each. Under 19 CFR 149.2, the ISF Importer files in English through a CBP-approved electronic system before the cargo is laden, so a missing ISF is a failure that exists before the vessel sails.
The FMC invoice rules that protect you
Since the FMC final rule published on February 26, 2024 (89 FR 14363), 46 CFR Part 541 sets minimum content and timing for every demurrage or detention invoice issued by an ocean common carrier, marine terminal operator or NVOCC. Five rules matter in a dispute:
- Missing information voids the obligation. Failure to include any required minimum information eliminates the billed party's obligation to pay the charge (541.5).
- Thirty-day issuance limit. The billing party must issue the invoice within 30 calendar days from the date the charge was last incurred, or the billed party is not required to pay (541.7(a)).
- NVOCC pass-through limit. An NVOCC must invoice within 30 calendar days from the date of the invoice it received (541.7(b)), and it gets an extra 30 days to dispute once its own billed party disputes (541.7(c)).
- Thirty-day dispute window. The billing party must allow at least 30 calendar days from invoice issuance to request mitigation, refund or waiver, and must attempt to resolve the request within 30 calendar days of receiving it (541.8).
- Correct billed party. The invoice must state the basis for why the billed party is the proper party of interest (541.6(a)(4)); an incorrect person can be re-invoiced only within the same 30 days (541.7(d)).
Every invoice must also carry the bill of lading number, the container number, the port of discharge for imports, the tariff or contract rule behind the daily rate, a contact for disputes, and two certifications: that the charges comply with FMC rules, and that the billing party's performance did not cause or contribute to the charges (541.6).
How the FMC judges whether a charge is reasonable
46 CFR 545.5 states the incentive principle: the Commission looks at whether demurrage and detention serve their purpose as financial incentives to promote freight fluidity. Four applications follow from it:
- Cargo availability: the Commission considers whether demurrage and free time relate to the cargo being available for retrieval.
- Empty return: detention imposed when empty containers cannot be returned is likely to be found unreasonable absent extenuating circumstances.
- Notice: the Commission considers whether, to whom and when notice of cargo availability is given.
- Government inspections: the Commission weighs extenuating circumstances when a customs exam holds the container.
The practical reading: a charge that accrues while the cargo is unavailable or the empty return is impossible is open to challenge.
Invoice audit checklist
46 CFR 541.6 groups the minimum content of an invoice into five blocks. Audit an invoice block by block before any payment:
| Block | Must appear |
|---|---|
| Identifying | Bill of lading number, container number, port of discharge (imports), basis for the billed party's liability |
| Timing | Invoice date, due date, free time in days, free time start and end dates, availability date (imports) or earliest return date (exports), dates charged |
| Rate | Total due, the tariff rule or contract section, the rate per day |
| Dispute | Contact, public website or QR code explaining the request process, timeframes |
| Certification | Charges comply with FMC rules; the billing party's performance did not cause or contribute to the charges |
A recomputation takes four numbers: the free time start date, the end date, the dates charged and the rate per day. Multiply the days charged by the daily rate in the cited rule and by the number of containers; a difference from the total due is an error to raise in the dispute.
A delay timeline
- Day 0: discharge. The availability notice goes out when the container can be retrieved.
- Free time days: the entry is released, the trucker collects the container.
- First day after free time: demurrage starts to accrue for a box still inside the terminal, per container per day.
- Collection: demurrage stops and detention starts for the box outside the terminal.
- Empty return: detention stops on the interchange receipt date.
- Last day of any charge: the 30-day invoice clock in 46 CFR 541.7 starts.
How to stop the clock
- Prepare the entry before arrival, not after. The broker needs documents days ahead, not on discharge day. A customs bond must already be in place.
- Book the drayage in advance and give the trucker the release requirements.
- Confirm the free days at quote stage and negotiate more where clearance is known to be slow.
- Have a warehouse slot booked for the day you plan to collect. See our Miami warehousing if you need staging near the port.
- Check the container weight against the road limit before pickup; an overweight box is refused at the gate and keeps accruing charges. The limits are in container weight limits.
- Return the empty promptly and keep the interchange receipt, because disputed returns are common.
Disputing a charge
Charges are disputable when the delay was caused by the carrier or terminal: no appointment availability, equipment not released, gate closures. Document everything with timestamps, keep the appointment attempts, and file the request inside the 30-day window in 46 CFR 541.8. The invoice itself must name the contact and the public website explaining which documents support a mitigation, refund or waiver request (541.6(d)).
A dispute file holds the invoice, the bill of lading, the availability notice and its timestamp, the appointment screenshots, the interchange receipt and the free time terms from the booking. Compare the invoice against the checklist in 541.6 first: a missing field ends the obligation without any argument on the merits.
FAQ
What is the difference between demurrage and detention?
Demurrage is for time inside the terminal; detention is for time with the carrier's container outside the terminal.
When does free time start?
On discharge or on availability, as the carrier's tariff states. The invoice must show the free time start date and the container availability date (46 CFR 541.6(b)), so the answer is on the document.
Are weekends counted?
If free time is expressed in calendar days, yes. Working day free time excludes weekends and holidays and is the less common structure.
Who pays demurrage, the shipper or the consignee?
The party the invoice identifies as the billed party, with a stated basis for why it is the proper party of interest (46 CFR 541.6(a)(4)). The Incoterm and the contract of carriage decide that basis; on imports it is the consignee.
Can demurrage be waived?
The billing party must provide a process to request mitigation, refund or waiver, a window of at least 30 calendar days from invoice issuance, and an attempt at resolution within 30 days of the request (46 CFR 541.8). Documented causes outside your control support the request.
How long does the carrier have to send the invoice?
30 calendar days from the date the charge was last incurred. After that the billed party is not required to pay (46 CFR 541.7(a)).
Does a customs exam stop the charges?
Not automatically. 46 CFR 545.5(c)(2)(iv) lets the FMC consider extenuating circumstances in a government inspection when judging whether the charge is reasonable, so the hold is evidence in a dispute and not a free pass.
Tight clearance windows on your lane? Ask us to structure the free time before the booking is placed.
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