Worldwide
Per diem and demurrage are not the same charge
Who bills which, what stops each clock, and why a carrier can owe one while the shipper owes the other.
The short answer
Demurrage is charged by the TERMINAL for a container that stays inside the gate after its free time. Per diem is charged by the STEAMSHIP LINE for their equipment — the box, and sometimes the chassis — while it is outside the gate. One clock runs while the container is in the port; the other runs while it is on the road or in a yard.
They are billed by different parties, stop for different reasons, and are disputed with different documents. Treating them as one line called "storage" is how an invoice becomes unarguable.
What stops each clock
| Charge | Billed by | Clock starts | Clock stops |
|---|---|---|---|
| Demurrage | Terminal / port | After the last free day, container still inside the gate | When the container leaves the terminal |
| Per diem | Steamship line | When the container leaves the terminal | When the empty is returned and RECEIPTED |
| Detention | The carrier, to their customer | When the driver has waited past the free time at a stop | When the driver leaves |
Where the money is lost
Per diem stops on the RECEIPT of the empty, not on its arrival. A driver who queues four hours and is turned away has returned nothing: the line keeps billing, and the only defence is a timestamped refusal. This is why an empty return diversion is a charge in its own right rather than a rounding error.
The last free day is the number both clocks pivot on, and it is the reason a prepull exists: pulling the container early and holding it in your own yard converts terminal demurrage — which you cannot control — into yard storage, which you can.
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