When free time runs out, demurrage covers a container that exceeds it at the marine terminal, while detention covers extended use of the equipment outside the terminal; in US practice detention is also billed as per diem. From the moment a loaded import container gates out, or an export unit is picked up, the desk owns the window until the empty comes back, so trucking, unpacking, and the empty return run are sequenced against the carrier's clock. The decision comes twice: at booking, where extended free time can be requested rather than absorbed as charges later, and at billing, where the desk reconciles pickup and return events against the invoice before paying or disputing it. Equipment detention is not driver detention, the waiting-time compensation paid when a truck driver is held beyond an agreed window, and it is not a customs hold, which detains the goods rather than charging for use of the carrier's container.
Glossary
Detention
The charge for keeping a carrier's container or equipment in use outside the marine terminal beyond the free time included in the carriage.