What is per diem in shipping?

A daily charge for keeping intermodal equipment — a container, a chassis or both — beyond the free time its provider allows. In the US it is set under the Uniform Intermodal Interchange Agreement.

Under the UIIA, the motor carrier that took the equipment. Its contract with the shipper then decides whether the charge is passed on.

How long does a provider have to bill per diem?

Under the UIIA, 60 calendar days from the date the equipment was returned, and the motor carrier has 30 calendar days to dispute the invoice.

Term

Per diem (container and chassis)

Per diem is the daily charge a US motor carrier pays when intermodal equipment — a container, a chassis or both — is not returned to its provider by the end of the free time. It is set in each provider's addendum to the Uniform Intermodal Interchange Agreement, and it counts as detention under US maritime rules.

Also called container per diem, chassis per diem, per diem chargesApplies in USUpdated 12 October 2026

What per diem is

The Uniform Intermodal Interchange Agreement (UIIA), run by the Intermodal Association of North America, defines per diem as the charge paid when intermodal equipment is not returned by the end of the allowable free time — whatever the provider calls it, per diem or a detention charge. Under the UIIA it is the motor carrier that is responsible for per diem, container use and chassis use charges.

Free days and the daily rate are set by each equipment provider in its own addendum to the UIIA.
The provider must invoice within 60 calendar days of the date the equipment was returned.
The motor carrier must dispute an invoice within 30 calendar days.
For ocean carriers' equipment, the Federal Maritime Commission treats per diem as part of demurrage and detention, so its reasonableness tests apply.

Worked example

Suppose a trucker picks up a container on 3 May and returns it empty on 12 May, and the provider's addendum gives 4 free days and charges USD 100 a day after them.

Days out = 9 · Chargeable = 9 − 4 = 5 × USD 100 = USD 500 · Invoice due by 12 May + 60 days = 11 July

How the first and last days count is set in the addendum — check it before checking the arithmetic.

Who finally pays is then a matter of the trucker's contract with the shipper. Where the delay was the shipper's — a warehouse that could not unload — the trucker will usually pass the per diem on.

When per diem is disputed

IANA's 2019 paper to the Federal Maritime Commission records the classic dispute: during the 2014–15 West Coast port labour disruption, ocean carriers charged per diem even though truckers could not return the equipment. The FMC's later interpretive rule asks whether a charge actually gives an incentive to move freight — a container that cannot be returned earns no such incentive.

The mistake people make

Letting per diem invoices pile up unchecked. Each provider's free days differ, the 30-day dispute window is short, and an empty container waiting for a return appointment that the terminal would not give is exactly the case the rules were written for.

FAQ