Fees and the clock
Demurrage vs detention: free time and the last free day
Demurrage is a fee on an import box left in the terminal past its last free day. Detention is billed for keeping the carrier's box too long after gate-out.
Updated Oct 30, 2026
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Demurrage and detention are two different late fees on a container. Demurrage is charged per day while your loaded import box sits in the terminal's yard after its last free day; its free time is counted from the day the box becomes available for pickup. Detention is charged for holding the ocean carrier's container too long once it leaves the terminal; that clock starts at gate-out and stops when the empty is returned. The last free day calculator counts the first clock for a given availability date, and "dwell fee" is a third term that is neither of these (dwell fee vs demurrage). 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.
When each clock starts
Take a loaded import box that becomes available for pickup on Monday, November 2, 2026, with 4 calendar free days. The free days run from the day after availability, November 3 through November 6, so the last free day is Friday, November 6. Demurrage can start on Saturday, November 7. A trucker who collects the box on Monday, November 9 takes it out 3 days past its last free day, and the weekend counts because the free days were calendar days. Counted in weekdays only, this box still has Friday, November 6 as its last free day, but a box available on Wednesday, November 4 would have Tuesday, November 10 instead of Sunday, November 8.
Gate-out on November 9 is also when the detention clock starts. The carrier's equipment free time runs from that day until the empty container is returned, so a slow unload at the warehouse can turn a box that already paid demurrage into one that pays detention too. The free-day counts, the daily rates and whether weekends count all come from the carrier's or terminal's tariff for that booking.
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. 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, use 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.
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 while your import container sits in the terminal yard past the free time. Detention is charged once you take the container away and hold the carrier's 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.
When does the demurrage clock start?
The day after the last free day. Free time is counted from the day the import box becomes available for pickup, so a box available on November 2 with 4 calendar free days has November 6 as its last free day, and demurrage can start on November 7.
When does detention start?
When the loaded container leaves the terminal gate. The carrier's free time for its equipment runs from gate-out until the empty is returned, and detention is charged for the days past that window.
Who charges demurrage, the terminal or the carrier?
Either can send the bill. Federal rules treat demurrage and detention as charges assessed by ocean carriers, marine terminal operators or ocean transportation intermediaries. Demurrage is the one tied to the terminal space a box occupies past its free time; detention is tied to the carrier's container off the terminal. 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.