What is demurrage in container shipping?

The three charges blur together because they all punish time, but they are billed by different parties for different things, and the line between them is a physical gate. Demurrage is charged for a loaded container that sits inside the terminal past its free time. Detention is charged for the carrier's equipment once it has left the terminal and is sitting at your yard or the customer's dock. Per diem is the daily charge on the container itself while you hold it out of the gate.

The simplest way to keep them straight: if the box is still behind the gate, it is demurrage. Once it crosses the gate, the clock becomes detention and per diem.

The number that decides demurrage is the last free day, and most back offices track it wrong. Last free day is set by the terminal, not the steamship line, and it is not fixed. It moves when the vessel's discharge date moves. A vessel that arrives two days late pushes the LFD two days later; a terminal that discharges early pulls it in.

So the LFD written down when the booking was made is a guess, and it is often already wrong by the time the container is available. A team tracking last free day in a spreadsheet is tracking a number that quietly changed underneath them.

Demurrage is not a rounding error. Rates step up the longer the container sits: free for the first few days, then a low daily rate, then a higher one, then a punitive tier. A single container missed for a week can run into four figures. One drayage customer traced a single missed container to roughly $9,000 in storage.

And the fee is only part of it. The real cost is the dispute, the reconciliation, and the conversation with the customer about who eats the charge.

Demurrage is almost never chosen. It is a container that dropped out of view. A delivery order arrives by email, someone keys it into the TMS, and the box joins a queue of a few hundred others. The failure is mundane: the container was on page two of the ready list, the LFD moved and nobody re-checked, the appointment could not be booked in time, or the order synced to the wrong customer and disappeared from the desk.

Every one of those is a data problem, not a trucking problem.

Preventing demurrage is a visibility problem before it is a scheduling problem. You cannot schedule a pull for a container you have lost track of. That means the delivery order has to land in the TMS without re-keying, the last free day has to update itself when the vessel does, and the containers approaching their free-time cliff have to surface on their own instead of waiting to be found.

When the list maintains itself, demurrage stops being a surprise and becomes an exception you act on.