Fees and the clock
Demurrage, detention and free time
Demurrage and detention are two different late fees on a container. Demurrage is what the terminal charges when your import box sits in its yard past the free time. Detention is what the carrier charges when you keep its container too long after you take it away. The last free day is the deadline before demurrage starts to accrue.
Updated Jul 10, 2026
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Demurrage and detention are two container fees importers dread, and they are not the same charge. Demurrage is what a marine terminal bills you when your import box sits in its yard past the free time. Detention is what the ocean carrier bills you when you hold its container too long after you have pulled it off the terminal. 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 is the terminal's money for its yard, detention is the carrier's money for its box, and a single late container can rack up both in sequence.
Why the queue is an early warning
- Ships awaiting berth
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. The federal rules on how carriers bill these charges tightened under the 2022 shipping-reform law, which requires carriers to publish their fee schedules and limits how far back they can invoice.
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.
Try it
Free days are counted starting the day after the container is available; the last free day is the last of those days, and the terminal's storage clock (demurrage) starts the next day. The 4-day default is a common figure, but free time varies by terminal, carrier and contract, so enter your own. The weekday option skips Saturday and Sunday only; it does not know port holidays or terminal closures, which some tariffs also treat as free. This is a day count on the numbers you enter, not fee, demurrage, or negotiation advice.
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Common questions
What is the difference between demurrage and detention?
Location. Demurrage is charged by the terminal while your import container sits in its yard past the free time. Detention is charged by the carrier once you take the container away and hold its equipment too long before returning it empty.
What is the last free day?
The last day you can collect an import container from the terminal before demurrage starts. Pull it by the last free day and you owe no storage; leave it past that day and the fee accrues per container per day.
Who charges demurrage, the terminal or the carrier?
The terminal, for the yard space the box occupies past its free time. Detention, by contrast, is the carrier's charge for holding its container off-terminal too long. A late box can incur both in sequence.
Does a busy port cause demurrage?
Not directly, but congestion raises the risk. When ships stack up offshore and terminals fill, boxes land in bunches and free time is harder to use before it runs out, so demurrage exposure builds across a complex.
The Dwell reports public US port-congestion data and explains how it works. It does not forecast congestion, volumes, fees, or ocean freight rates, and it is never routing, booking, or fee advice: it does not tell a reader which port to use, when to book, when to pull a container, or how to handle a demurrage or detention charge. Figures are attributed to BTS, MARAD, the FHWA, the STB and the port authorities as published.