Detention, demurrage and per diem are three charges that all bill for the same underlying thing: time. Detention bills you for holding a driver and power unit. Demurrage bills you for holding cargo or a container inside a facility past its free time. Per diem bills you for holding the equipment itself after it leaves that facility. Different assets, different clocks, different documents that prove or disprove the charge.
The confusion is not your fault. Carriers, terminals and railroads use the words inconsistently, and the same invoice can carry two of them under one label. An ocean carrier’s “detention” and a truckload carrier’s “detention” are not the same charge and are not governed by the same rules. A rail “demurrage” and a marine terminal “demurrage” are also different animals.
The one-sentence definition of each
What separates them is which asset is tied up, and where.
Detention. A carrier bills detention when its driver and tractor sit at your facility past the free time in the agreement. The asset is the truck and the human. It accrues at the gate, on the yard, or at the dock, and it stops when the driver leaves.
Demurrage. A terminal, port or railroad bills demurrage when cargo or a container sits on their property past its free time. The asset is their real estate, and it accrues while the box is still inside the yard.
Per diem. The equipment owner (steamship line, railroad, container lessor, or a trucking company that owns the chassis) bills per diem when you keep their equipment beyond the allowed days. The asset is the box, the chassis or the trailer. It accrues while the equipment is in your possession, off their property.
The clean mental model: demurrage is rent for their ground, per diem is rent for their steel, detention is the bill for their driver’s stopped clock.
The overlap that trips people up: on an ocean move, the carrier often calls the off-terminal equipment charge “detention,” not per diem. It has nothing to do with a driver sitting anywhere. When an ocean invoice says detention, read it as container-out-of-terminal time until you have confirmed otherwise.
The comparison table
| Detention (truckload/LTL) | Demurrage (rail or marine terminal) | Per diem (equipment) | |
|---|---|---|---|
| What is tied up | Driver and tractor | Terminal or rail yard ground | Container, chassis or trailer |
| Where it accrues | At your dock or gate | Inside the terminal or rail yard | Anywhere off the terminal |
| Who bills | Motor carrier, often through a broker | Marine terminal operator, ocean carrier, or railroad | Ocean carrier, railroad, chassis pool or lessor |
| Typical unit | Per hour or fraction after free hours | Per container per day after free days | Per unit per day after free days |
| Clock start | Contractual event: arrival, appointment, or check-in | Cargo availability or placement | Gate-out from the terminal |
| Clock stop | Departure from the facility | Gate-out or pickup | Gate-in (empty return) |
| What settles a dispute | Timestamps and the free-time clause | Availability and placement records | Gate-out and gate-in records |
The bottom row is the whole audit. Every one of these charges is a subtraction problem: end time minus start time, minus free time, times a rate. Disputes almost never turn on the rate. They turn on which event started the clock and whether the record proves it.
Detention: the truckload version
Detention is the only one of the three where a person, not just an asset, is waiting. That is why it carries the strongest economic argument and the weakest documentation.
The economic case is documented. The DOT Office of Inspector General’s 2018 report on driver detention estimated that a 15-minute increase in average dwell time raises the average expected crash rate by 6.2 percent, and that detention reduces for-hire truckload driver annual earnings by $1.1 to $1.3 billion and truckload carrier net income by $250.6 to $302.9 million per year. That is the honest backdrop for any detention dispute: the charge exists because the underlying cost is real.
What detention does not have is a rulebook. No federal regulation sets free time, sets a detention rate, or requires a facility to pay it. Whether detention is owed on a domestic truckload move is a contract question, decided by the rate confirmation, the transportation agreement, and whatever rules tariff that agreement incorporates. Arguing that a carrier “cannot” bill detention because of a regulation is the fastest way to lose credibility in a dispute thread.
The contractual variable that decides most detention arguments is the clock trigger, and it is rarely the same across two carriers. Arrival at the gate, check-in with the guard, appointment time, and driver-app geofence entry produce meaningfully different bills on the same load, as worked through in when detention free time actually starts.
Demurrage: two charges wearing one word
Demurrage on an ocean move and demurrage on a rail move are both ground rent, but the systems differ.
Marine terminal demurrage accrues on a container sitting inside the terminal after its free days expire. Free time typically starts when the cargo becomes available, which is a defined event, not the day the vessel docked. Whether the container was actually available for pickup during the days billed is the single most productive question to ask.
Rail demurrage accrues on railcars held past free time at an industry track or a terminal. It runs on the railroad’s published demurrage tariff and the private agreements around it. Rail demurrage terms, including constructive placement (the railroad wanted to place the car, you could not receive it), are contractual and tariff-based rather than set by a single federal rule you can quote back.
For ocean moves specifically, there is a real federal billing rulebook, covered below. For rail and for domestic truckload, there is not.
Per diem: rent on the equipment
Per diem starts when you take equipment out and stops when you bring it back. The two data points that decide the entire charge are the gate-out timestamp and the gate-in timestamp, both of which live in the terminal or railroad’s system rather than yours.
That asymmetry is the whole problem. When a per diem invoice looks wrong, you are almost always disputing a return date, and the counterparty holds the return record. The practical defense is to build your own copy at the moment it happens: interchange receipts (EIR), the driver’s gate ticket, the trucker’s dispatch record. A per diem dispute filed with your own gate-in receipt attached resolves quickly. One filed with an assertion that “we returned it Tuesday” does not.
Two per diem patterns worth auditing every time:
- Return refused, clock kept running. The terminal turned the empty away for a capacity or vessel-window reason, and per diem accrued for days you had no way to stop. Your evidence is the refusal record and the driver’s trip log for the attempted return.
- Chassis billed separately and simultaneously. Container and chassis can come from different owners with different free time and rates. Two invoices for the same days is not automatically a duplicate, but confirm they are genuinely two assets and not one billed twice, using the pattern in how to catch a duplicate freight invoice.
Who actually owes each one
The billed party and the responsible party are frequently not the same, and this is where money is lost quietly.
Detention. The carrier bills whoever tendered the load. On brokered freight that is the broker, who then passes it to the shipper. The party that caused the delay may be a third one entirely: your customer’s receiver, running two hours behind on the door. Whether the charge flows through to them depends on your terms with them, not on your terms with the carrier. Brokers get squeezed here constantly.
Demurrage. The terminal or railroad bills the party on file, usually the consignee or its agent. Whether that party is the right one depends on the delay’s cause: a customs hold, a late release from the ocean carrier, a chassis shortage, and a receiver who never scheduled the pickup all produce the same invoice and very different answers about responsibility.
Per diem. The equipment owner bills the party that took the equipment out, typically the motor carrier at the gate, who passes it upstream.
One statutory note for consignees: under 49 U.S.C. 13706, a consignee acting as an agent who gives the carrier written notice of its agency status before delivery is liable only for the rates billed at delivery, with the beneficial owner liable for additional charges. A consignee that misidentifies the beneficial owner stays liable. The notice has to be written, and it has to be before delivery.
The evidence standard for each charge
This is the part worth keeping. Each charge is proved or disproved by a different record.
| Charge | What the biller must show | Your strongest counter-record |
|---|---|---|
| Detention | Arrival and departure timestamps tied to this driver and this load, plus the free-time clause | Gate log, security check-in, receiving door log, appointment record, your own dock scan times |
| Marine demurrage | Cargo availability date and the pickup date, plus applicable free days | Availability notices, hold status (customs, line, terminal), appointment refusals, trucker attempt records |
| Rail demurrage | Placement or constructive placement date and release date | Your own railcar placement log, notification records, plant capacity documentation |
| Per diem | Gate-out and gate-in timestamps for that equipment number | Equipment interchange receipts, return gate tickets, refusal documentation, driver trip records |
Detention has the weakest paper trail, which is why it produces the most disputes per dollar billed. The six documents that decide a detention argument are laid out in the documents that win a detention dispute, and when the POD comes back with no in and out times at all, the reconstruction path is in disputing a detention charge with no POD times.
Where regulation actually helps you
Be precise about this, because overstating it is the most common mistake in these disputes.
Ocean demurrage and detention have a federal billing rulebook. 46 CFR Part 541 sets billing requirements and practices. Under 46 CFR 541.7, the billing party must issue a demurrage or detention invoice within 30 calendar days from the date the charge was last incurred. Under 46 CFR 541.8, the billed party gets at least 30 calendar days from the invoice issuance date to request mitigation, refund or waiver, and the billing party must attempt to resolve that request within 30 calendar days of receiving it, or later if both parties agree. Under 46 CFR 541.6, the invoice itself has to state those timeframes. An invoice that arrives late, or that does not tell you how long you have to contest it, has a defect on its face.
Domestic truckload detention does not. What federal law gives you on the motor carrier side is timing and itemization, not free time or rates. Under 49 U.S.C. 13710, a carrier billing charges additional to those originally billed must do so within 180 days of your receipt of the original bill to preserve its collection rights, and you must contest a bill within 180 days of receipt to preserve your right to challenge it. Under 49 CFR 373.103, a freight or expense bill has to show the exact rates assessed and the total charges due with the nature and amount of each charge. A detention line reading “ACC 320.00” with no hours and no rate does not meet that description.
If you already paid it, you are filing an overcharge claim, not disputing an invoice, and a different clock starts. Under 49 CFR 378.8, the processing carrier must pay, decline, or settle a written overcharge claim within 60 days of receipt absent a written agreement to extend. The full set of these windows sits in the freight billing deadlines reference.
The five questions that resolve almost any time-based charge
Run these in order. They work on all three because all three are the same arithmetic.
- Which charge is this, really? Read the equipment number and the location, not the label. An ocean “detention” line is usually equipment time off-terminal.
- What event starts the clock, per the agreement? Name the document and the clause. If nobody can point to one, the charge has no defined start and the dispute is already half won.
- What is the free time, and does it run in hours, business days or calendar days? Calendar versus business days on a weekend move is often the entire dispute.
- What records prove the start and stop times? Ask for the biller’s record and produce your own. Two independent records that agree end the argument.
- How was the elapsed time converted to money? Rounding conventions do real damage, and almost nobody checks the math: see detention billed in 15-minute versus hourly increments.
What to do this week
- Pull every time-based charge from last month and sort it into the three buckets by asset, not by the word on the invoice.
- For each bucket, find the governing clause: the rate confirmation for detention, the terminal or rail tariff for demurrage, the interchange or equipment agreement for per diem.
- Confirm each invoice states hours or days, the rate, and the start and stop timestamps. If it does not, request itemization before arguing merits.
- On ocean charges, check the invoice date against the last-incurred date and check whether the invoice states your mitigation window. Both are required by 46 CFR Part 541.
- Capture your own timestamps at the gate, at the door and at the return. The party with a contemporaneous record wins these, and the record has to exist before the invoice does.
None of this makes time-based charges go away, and it should not. A driver who waited four hours waited four hours. The goal is that the invoice reflects what happened, on the clock both sides agreed to, with arithmetic anyone can reproduce.
Sources
- 46 CFR Part 541, Demurrage and detention billing requirements and practices (Cornell LII)
- 46 CFR 541.6, Required invoice contents including mitigation timeframes (Cornell LII)
- 46 CFR 541.7, Invoice must issue within 30 days of the charge last incurred (Cornell LII)
- 46 CFR 541.8, Billed party’s 30-day window to request mitigation, refund or waiver (Cornell LII)
- 49 CFR 373.103, What a freight or expense bill must show (Cornell LII)
- 49 CFR 378.8, Overcharge claims resolved within 60 days (Cornell LII)
- 49 U.S.C. 13710, Billing and contesting windows (Cornell LII)
- 49 U.S.C. 13706, Liability of consignees and agents (Cornell LII)
- DOT OIG Report ST2018019, Driver detention economics and crash-rate effect (U.S. DOT Office of Inspector General)