Demurrage and detention may appear on the same invoice or under the shorthand "D&D". Many customers, and plenty of new ops staff, treat them as one charge. They are not. They usually cover different stages of an ocean import, start at different moments and are stopped by different actions under the applicable tariff or contract.
Getting the difference right matters, because the fix for each one is different. This guide explains where demurrage and detention apply, when each clock starts, who usually pays, how "per diem" fits in, and how to track both on every container.
What's the difference between demurrage and detention?
Direct answer: Demurrage generally applies while a full import container remains in the terminal after free time. Detention generally applies after the container leaves the terminal and the empty is not returned within its separate free-time window. Pickup usually stops demurrage; returning the empty usually stops detention under the applicable carrier tariff.
In common industry usage, demurrage is about terminal time and detention is about equipment time outside the terminal. A single shipment can incur both, one after the other, but the carrier's tariff or contract controls the exact definitions and clock rules.
Demurrage vs detention at a glance
| Demurrage | Detention | |
| Where the container is | Inside the terminal, still full | Outside the terminal, with the trucker or consignee |
| When the clock starts | After terminal free time ends under the applicable tariff, often the day after the last free day | After out-of-terminal equipment free time ends under the applicable tariff |
| What stops it | Picking the container up | Returning the empty to the designated location |
| Who usually bills it | The ocean carrier or marine terminal | The ocean carrier (the container owner) |
| Common causes | Late documents, holds, unpaid charges, no pickup appointment | Slow unloading, no empty return appointment, trucker delays |
How do US rules treat demurrage and detention?
For U.S. federal billing rules, the two are grouped. The Federal Maritime Commission's rules in 46 CFR Part 541 define "demurrage or detention" together as charges, including per diem charges, assessed by ocean carriers, marine terminal operators or NVOCCs for the use of terminal space or shipping containers, but not freight charges.
Those federal billing requirements apply to both charge types. VOCCs and marine terminal operators generally must issue invoices within 30 calendar days after the charges were last incurred; NVOCCs have 30 calendar days from the date of the invoice they received. The billed party must receive at least 30 calendar days to request mitigation, refund or waiver, and the billing party generally must attempt resolution within 30 calendar days unless both parties agree to longer. In September 2025, the D.C. Circuit set aside §541.4, the provision that limited who could be billed; the FMC says the other provisions remain in effect while it revisits that issue. Our guide to demurrage charges covers those rules in more detail.
What is per diem, and is it the same as detention?
"Per diem" simply means a daily charge. In U.S. ocean shipping it often refers to the daily charge for keeping a carrier's container, or sometimes related equipment such as a chassis, beyond free time. It is frequently used as another name for detention, but the label is not universal.
Some carriers and truckers use per diem differently, for example for a chassis charge billed to the trucker. Because the terms vary, the safest approach is to read the carrier's tariff and your trucking agreement and use their definitions on invoices and customer notices.
When does the clock start for demurrage and for detention?
Demurrage commonly begins after the terminal free-time period ends, often the day after the last free day. The start event, weekend and holiday treatment, and last free day calculation depend on the applicable carrier or terminal tariff and the cargo-availability rules. Our guide to last free day (LFD) in shipping explains how that date is calculated and why it moves.
Detention starts after the container has left the terminal and its own free time has run out. How many days you get, and whether weekends count, again depends on the carrier's tariff or your contract. The practical point is that detention free time is a separate window. Picking up on the last free day does not give you more detention days.
Who pays demurrage and detention?
Responsibility depends on the applicable tariff, bill of lading, service or storage agreement, and any valid pass-through terms. In the United States, the D.C. Circuit set aside §541.4 in September 2025, so the rule's former restriction on who could be invoiced is no longer in force; the FMC says it is revisiting that issue while the rest of Part 541 remains effective.
Detention often creates more disputes than demurrage, because more parties are involved once the container leaves the terminal: the trucker, the consignee's warehouse and sometimes a chassis provider. Clear records of when the container was picked up, delivered, unloaded and returned make those disputes much easier to settle.
Why do teams confuse demurrage and detention, and why does it matter?
The confusion is understandable. The charges often appear on one invoice, the same free days language is used for both, and some carriers bundle them into a single "combined free time" offer. But mixing them up leads to the wrong fix:
- If the problem is demurrage, the fix is upstream: documents, customs, payment and pickup booking.
- If the problem is detention, the fix is downstream: unloading time at the warehouse, empty return appointments and trucker capacity.
It also leads to weak disputes. A charge can only be challenged well if you know which clock it belongs to and have the dates that prove what happened.
How do you track demurrage and detention on every container?
For each container, keep these dates in one place:
- The discharge or availability event used by the applicable tariff to start terminal free time.
- Last free day, the deadline for pickup.
- Gate-out date, when the full container actually left the terminal.
- Detention free time end date, the deadline for returning the empty.
- Empty return date, when the container actually went back.
With those five dates, you can see risk early, warn customers in time, and check every D&D invoice against what really happened. Without them, invoices are hard to check and disputes are hard to win.
How can automation help with demurrage and detention?
Most of these dates arrive in carrier updates and terminal notices, not in your system. An AI teammate can read those updates as they come in, keep the last free day, gate-out and empty return current on each shipment, and flag containers that are approaching either deadline. When a D&D invoice arrives, it can link each charge to the right shipment and highlight days that do not match the recorded dates, so an operator can decide whether to pay or dispute.
Where NavLogic fits
NavLogic is the AI teammate built for freight operations. For ocean imports it monitors ETA, holds, last free day, gate-out and empty return across carrier updates, and reads carrier and D&D invoices so each charge is categorized and linked to the right shipment. When a container is at risk, it brings the issue to the right operator with the context attached.
Frequently asked questions
Is demurrage the same as detention?
No. In common industry usage, demurrage applies while the full container remains in the terminal after free time. Detention applies after gate-out when the empty is not returned within its separate free-time window. The applicable tariff controls the exact terms.
Which comes first, demurrage or detention?
For a standard import sequence, demurrage exposure typically comes first while the container remains in the terminal. Detention can follow after gate-out if the empty container is not returned within its free time.
Is per diem the same as detention?
Often, but not always. In U.S. ocean shipping, per diem frequently means a daily equipment charge after free time and may be used as another name for detention. It can also refer to chassis or other equipment charges, so check the tariff and contract.
Can you be charged demurrage and detention on the same container?
Yes. A container can sit in the terminal past its last free day, incurring demurrage, and then be returned late after pickup, incurring detention.
Who is responsible for detention charges?
Responsibility depends on the tariff, bill of lading, service or storage agreement, pass-through terms and current law. Do not assume that the importer, consignee, trucker or NVOCC is automatically the proper billed party. Keep gate-out, delivery and return records for every container.
How do you avoid detention charges?
Plan unloading before the container arrives, book the empty return early, confirm the correct return location, and track the detention free time for each container so late returns are caught before the deadline.
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