Demurrage, detention and free time

Demurrage and detention are two container fees importers dread, and they are not the same charge. Demurrage is the charge for your import box sitting in the terminal's yard past the free time. Detention is the charge for holding the ocean carrier's container too long after you have pulled it off the terminal. Federal rules cover both whether the ocean carrier, the terminal operator or an ocean transportation intermediary sends the bill. One is about occupying the terminal's space. The other is about tying up the carrier's equipment. The line between them is where the box physically is.

Free time and the last free day

Every import container comes with free time, a set number of days you can leave the box on the terminal at no charge while you arrange to collect it. The last free day is the final day of that window. Pull the container by the last free day and you owe nothing. Leave it past that day and demurrage starts to accrue, billed per container per day until the box moves. Free time is granted by the carrier and it varies by contract and by terminal, so the day count is not a fixed rule.

Demurrage: the terminal's clock

Demurrage runs while the loaded import box is still inside the terminal past its free time. The cause is usually downstream, a missing truck appointment, a full warehouse, a customs hold, anything that keeps the box from being collected. The fee climbs each day, and in a congested yard it can climb in tiers. The point to hold onto is that demurrage is terminal storage, charged for the space the box occupies, and it stops the moment the container leaves the gate.

Detention: the carrier's equipment

Detention picks up where demurrage leaves off. Once you take the loaded container out through the gate, the free-time clock for the carrier's equipment starts. You unload the box at your facility and you are expected to return the empty within another free window. Hold it too long and the carrier charges detention for the extended use of its container. Demurrage pays for the terminal's yard space, detention for the carrier's box, and a single late container can rack up both in sequence.

Why the queue is an early warning

The ship queue above is a leading read on fee exposure. When vessels stack up offshore, boxes land in bunches, terminals fill, and free time gets harder to use before it runs out. A rising queue is not a fee, but it is the condition under which demurrage risk builds across a complex. Federal billing rules tightened too: since May 28, 2024, a Federal Maritime Commission rule has required a demurrage or detention invoice within 30 days of the last day the charge was incurred, showing the free-time dates and, for imports, the container availability date (46 CFR part 541).

The Dwell explains how these fees work and shows the congestion that raises the risk of them. It does not tell you how to count the free days on a specific booking, dispute a charge or negotiate one. For the day count itself, see the last free day calculator. For the milestones the clock runs on, see the clocks an importer watches.

The dates these fees run on, discharge, available for pickup, the last free day and gate-out, each come from a specific system on a real booking; container milestone tracking covers where to find each one. Two terms get confused with the charges here. Trucking uses "detention" for a different clock entirely, a truck held at a shipper's or receiver's dock, covered in dwell time in trucking. And "dwell fee" is not a standard tariff charge at all; dwell fee vs demurrage explains where the term comes from.