Demurrage and Detention Explained

(reading time: 4 mins)

If you move containers by sea, you have probably met the two unpleasant words demurrage and detention. For many companies these charges appear as a surprise, often weeks after the cargo has moved, and they can easily wipe out the profit on a shipment. Understanding what they mean and how they arise is the first step towards avoiding them.

Demurrage vs detention – what is the difference?

Although the two terms are often used together, demurrage and detention are not the same thing. Demurrage is a fee charged by the shipping line when a full container stays too long inside the port or terminal. On imports this means the container remains in the terminal after discharge beyond the free days; on exports it sits in the terminal too long before being loaded on the vessel.

Detention, on the other hand, relates to time outside the terminal. It is the fee charged when the shipping line’s container stays too long at your warehouse, on the trucker’s chassis, or in a depot. In both cases you are essentially paying rent for using the container and the space for longer than agreed.

Why do these charges exist at all?

Ports and shipping lines are not set up to be long-term storage providers. They need containers to move quickly so that terminals do not clog up and ships are not delayed. To encourage this flow, every shipment is given a certain amount of free time in the tariff. After these free days expire, daily demurrage or detention charges start to apply. The daily rates often rise in stages, which is why a delay that starts small can grow into a surprisingly high invoice.

Where companies most often get caught

In day-to-day work we see the same patterns repeating. Extra port costs frequently appear when customs clearance is not ready on time, for example because documents, HS codes or licences are incomplete. Another common issue is that trucking is arranged only after the vessel has already arrived, instead of being booked in advance. Confusion around Incoterms also plays a role: if it is not clear who is responsible for local charges, customs and delivery, containers may simply sit while the parties argue.

On the export side, rolled or delayed vessels can cause demurrage when containers enter the terminal too early and then wait for the next available ship. Sometimes companies use the container as a temporary warehouse at their own site because they lack storage space. While this may feel convenient in the short term, it usually generates high detention fees.

How demurrage and detention are calculated

Every shipping line and port has its own detailed tariff, but the logic behind them is similar. A certain number of free days is included in the rate. After that, a fixed amount is charged per container for each extra day the box stays where it should not be, whether in the terminal (demurrage) or outside it (detention). The charges differ by container type and size, and they often become more expensive after the first few days. For a company operating on tight margins, even a handful of extra days can create a painful, unexpected cost.

Practical ways to avoid extra port costs

The good news is that most demurrage and detention is avoidable with planning and clear communication. It helps enormously to know your exact free time before the shipment starts and to treat the last free day as a hard deadline. Customs documents, licences and HS codes should be prepared as early as possible so that clearance can take place immediately after arrival. Aligning trucking and warehouse capacity with the vessel’s ETA is equally important; if the truck is booked and the warehouse is ready, the container does not have to wait in the terminal.

Clear responsibilities are another key factor. Everyone involved needs to understand the chosen Incoterm and what it means in practice: who pays which local charges, who books the truck, and who is responsible for customs and documents. If you need extra storage, it is usually cheaper to unpack the container into a warehouse and return the empty box than to keep the container on site and pay detention. Finally, it is wise to work with a forwarder who monitors free days and warns you early when a shipment is drifting towards demurrage or detention, giving you time to react rather than discovering the problem through an invoice.

How a forwarder can help

At SME-Europe we see demurrage and detention not just as annoying line items, but as signs that planning or communication could be improved. Our role is to explain local port terms and free-time conditions in plain language, map out the critical dates together with you, and coordinate with truckers, terminals and customs brokers so that containers keep moving. We actively monitor free days and highlight potential issues before they become costs.

Demurrage and detention will probably always exist in maritime transport, but they do not have to be a regular feature of your shipping budget. With the right preparation and a forwarder who treats your cargo as carefully as you do, extra port costs become the exception rather than the rule.