Detention, also called per diem, is a fee that carriers may charge when a shipping container remains outside the port or terminal beyond the allowed free time.
For import shipments, the container leaves the terminal for unloading. The party responsible for the container needs to return it to the designated location within the agreed free period. If the container stays out longer, the carrier may charge detention for the additional days.
Unlike demurrage, which generally applies while a container remains inside the port or terminal, detention applies after the container leaves the terminal.
Detention does not normally start as soon as the container leaves the port. The shipping line usually allows a period of free time for delivery, unloading, and empty container return.
The basic timeline looks like this:
CONTAINER PICKUP → FREE TIME → UNLOADING → EMPTY RETURN
If the empty container is not returned within the allowed period, detention charges may begin.
The amount of free time varies. It can depend on the carrier, location, container type, and shipping agreement. Check the applicable terms before arranging delivery.
Both charges relate to keeping a container beyond the allowed free time. The main difference is where the container is located.
| Demurrage | Detention |
|---|---|
| Container remains at the port or terminal | Container has left the port or terminal |
| Related to terminal free time | Related to equipment free time |
| May apply while cargo waits for pickup | May apply while the container is outside the terminal |
| Stops based on the applicable terminal/carrier terms | Stops when the container is returned under the applicable terms |
A simple way to remember the difference:
Inside the terminal → Demurrage
Outside the terminal → Detention
For more detail, read our guide to demurrage charges.
Shipping lines usually calculate detention according to the number of chargeable days and the applicable daily rate.
Daily Detention Rate × Chargeable Days = Detention Charge
For example, suppose a container has five days of free time. If the applicable return occurs three days after that period ends, detention may apply to those three additional days.
This is only an example of how the calculation works. Actual rates and charging rules vary by carrier, container type, location, free-time agreement, and number of overdue days.
Always check the applicable terms for your shipment instead of relying on a fixed detention rate.
There is no single answer for every shipment.
The shipping agreement, carrier terms, and delivery arrangement determine who pays detention charges.
For example, unloading may take longer than planned, or delivery delays may prevent the empty container from reaching the return location on time.
Shippers and consignees should confirm the available free time, return deadline, and applicable terms before the container leaves the terminal.
Detention often comes down to timing. A few practical checks can reduce the risk of unexpected charges.
Know Your Free Time
Confirm how many free days apply and when the free period ends.
Prepare for Unloading
Make sure the receiving location can accept and unload the container as planned.
Plan the Empty Return
Check where and when the empty container needs to be returned.
Respond to Schedule Changes
Delivery, warehouse, or trucking delays can affect the return plan. Review the timing again when the schedule changes.
1. Is detention the same as demurrage?
No. Demurrage generally applies when a container stays at the port or terminal beyond the allowed free time. Detention generally applies after the container leaves the terminal and stays out too long.
2. When does container detention start?
Detention may start when the agreed equipment free time expires. The carrier’s terms and shipping arrangement determine the exact start point.
3. Can you avoid detention charges?
Careful planning can reduce the risk. Confirm the return deadline, arrange unloading in advance, and plan the empty container return. Always check the carrier’s terms for your shipment.
ASLG can help arrange sea freight from China based on your cargo, route, container requirements, and delivery plan. Explore our sea freight services or discuss your shipment with our team.
