Detention vs demurrage vs per diem: who pays what
Three clocks, three billers, three sets of rules.
Reviewed October 8, 2026
Short answer: Truck detention is what a trucking carrier charges when its driver is held at your dock past the free time. Demurrage usually means an ocean carrier's or marine terminal's charge when an import container sits at the terminal past its free days. Per diem, often called container detention, is the daily charge when the carrier's container or chassis stays out of the terminal, for example in your yard, past its free time. They're three separate clocks: a warehouse can run up all three on a single container.
Side by side
| Truck detention | Demurrage | Per diem / container detention | |
|---|---|---|---|
| What is waiting | The driver and truck | The container, at the terminal | The container or chassis, outside the terminal |
| Who usually bills | The trucking carrier (or broker) | Ocean carrier or marine terminal | Ocean carrier, or the equipment provider under the UIIA |
| Clock starts | When contract free time at pickup or delivery runs out | When the terminal free days run out | When free time after pickup from the terminal runs out |
| Set by | Your contract with the carrier or broker | Carrier or terminal tariff; FMC billing rules apply | Carrier tariff or the provider's UIIA addendum; FMC or UIIA billing rules apply |
| What stops it | The truck leaving your dock | The container leaving the terminal | The empty going back where the provider says |
"Usually" matters here. Terms vary by contract and tariff, and the FMC's rule lumps demurrage and detention under one definition (below). Read the invoice for what it's actually charging for.
What the FMC rule says about demurrage and detention
For ocean shipping, the Federal Maritime Commission defines "demurrage or detention" as "any charges, including 'per diem' charges, assessed by ocean common carriers, marine terminal operators, or non-vessel-operating common carriers related to the use of marine terminal space (e.g., land) or shipping containers, but not including freight charges" (46 CFR 541.3). Its billing rule, in effect since May 2024, sets deadlines on both sides:
- The billing party must issue the invoice within 30 calendar days of the date the charge was last incurred. If it doesn't, "the billed party is not required to pay the charge" (46 CFR 541.7).
- The billed party gets at least 30 calendar days from the invoice date to request mitigation, refund or waiver, and the billing party must try to resolve the request within 30 days (46 CFR 541.8).
- An invoice missing the required minimum information doesn't have to be paid (46 CFR 541.5; final rule, Feb 2024).
Per diem under the UIIA
When a trucking company picks up intermodal equipment under the Uniform Intermodal Interchange and Facilities Access Agreement, per diem is defined as the "charge to be paid when intermodal Equipment is not returned by the end of the allowable free time." The agreement adds that a charge fitting that description is per diem "whether or not it is referred to as Per Diem, a detention charge, or otherwise." Free time and rates come from each equipment provider's addendum. The provider must invoice within 60 calendar days of the equipment's return, or it loses the right to recover the charge (UIIA, effective May 5, 2026). The motor carrier is billed under the UIIA, and whether that cost passes through to you depends on your contract with them.
Truck detention is a contract term
No federal rule sets a truck detention charge. The free time, the hourly rate and the proof required are in your contract with the carrier or broker. The do shippers have to pay truck detention? answer covers it in detail, and the detention and free time calculator shows when a given truck's free time runs out.
Checklist: which charge is on this invoice?
- Who sent it? A trucking company or broker points to truck detention. An ocean carrier, NVOCC or terminal points to demurrage or detention under the FMC rule. An equipment provider billing your trucker points to UIIA per diem.
- What was waiting? A driver at your dock, a container at the port, or a container or chassis in your yard.
- Which dates? Check the start and end of the charge against your own gate records: when the unit arrived at your gate and when it left.
- Is it on time and complete? For ocean charges, check the 30-day issue window and the required information. For UIIA per diem, check the 60-day window.
- Can you prove the times? Your gate-in and gate-out timestamps are your side of every one of these disputes. The records you need to win a detention claim answer lists them.
FAQ
What is per diem in trucking?
Under the Uniform Intermodal Interchange and Facilities Access Agreement (UIIA), per diem is the charge paid when intermodal equipment is not returned by the end of the allowable free time. The UIIA says it counts as per diem whether it is called per diem, a detention charge, or something else.
How long does an ocean carrier have to send a demurrage or detention invoice?
Under the FMC's rule at 46 CFR 541.7, 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 it. Under 46 CFR 541.8, the billed party gets at least 30 calendar days from the invoice date to request mitigation, refund or waiver.
Is there a federal law that makes shippers pay truck detention?
No federal rule sets a truck detention charge. Truck detention is a contract term between the shipper or receiver and the carrier or broker: the free time, the rate, and what proof is needed.
Have your own gate times ready.
Every one of these charges comes down to when a unit arrived and left. With Vantage, the guard logs gate in and out on a phone, with a timestamp on every record and a photo whenever the camera is used. The Free plan is $0 for 3 users, 1 yard and 100 gate transactions a month. No card.
This page explains terms and cites the rules. It is not legal advice; your contracts and tariffs govern. Related: reduce detention charges at the dock · why detention invoices don't get paid · detention dispute letter