Demurrage vs detention vs per diem: what each charge means
Updated 27 October 2026 · 7 min read
Short answer. Demurrage is charged for the time a container stays inside the port or terminal after its free time has run out. Detention is charged for the time a container stays outside the terminal, in the hands of the shipper, consignee or haulier, after its free time. Per diem is a daily charge for using a container: in US trucking it is often another name for detention, and in container leasing it is the daily rental rate of a leased box.
The three charges side by side
| Demurrage | Detention | Per diem | |
|---|---|---|---|
| Where is the container? | Inside the terminal or port | Outside the terminal | Outside the terminal (in use) |
| What is being paid for? | Use of terminal space and of the container while it waits | Use of the container while it is away | Use of the container, day by day |
| Who usually bills it? | Shipping line or terminal | Shipping line | Shipping line (detention sense) or container lessor (leasing sense) |
| When does the clock start? | When the free time in the terminal ends | When the free time outside the terminal ends | At gate-out (or after free days, depending on the contract) |
| When does it stop? | When the full container leaves the terminal (import) or is loaded (export) | When the empty container is returned to the depot or terminal | When the container is returned (off-hire) |
Demurrage
For an import, a full container is discharged from the vessel and sits in the terminal until it is picked up. The carrier grants a number of free days. Every day after that is billed as demurrage. For an export, demurrage can apply when a full container is delivered to the terminal too early or waits for a later vessel.
Typical causes are customs holds, missing documents, unpaid freight and congested terminals. The free time and the daily rate depend on the carrier, the port and the contract, and the rate usually increases by tiers (for example days 1 to 5, then days 6 to 10, then beyond).
Detention
Once the full container leaves the terminal (gate-out), it is out of the carrier's yard but still the carrier's equipment. The consignee unloads it, and the empty box must be returned to the depot named in the return instructions. If this takes longer than the free time outside the terminal, the carrier bills detention for each extra day, until the empty container is gated back in.
Some carriers merge both clocks into a single "combined" free time covering the days inside and outside the terminal. Read the tariff or the contract to know which model applies.
Per diem: two meanings
- In shipping and trucking (US usage): per diem is the daily charge for keeping a carrier's container or chassis beyond the free time. In practice it is detention under another name.
- In container leasing: per diem is the daily rental rate a lessee pays a lessor for each container on hire. A lease usually combines a number of free days with a per diem rate: once the free days of a container are used up, each additional day is billed at the per diem rate until the container is returned.
How the days are counted
Charges are counted in calendar days, and the contract says whether the first and the last day both count. A common rule, and the one used in Krak Stack for leasing, counts both ends:
A container picked up on 1 March and returned on 9 May is on hire for 70 days (31 + 30 + 9). With 60 free days and a per diem of 2 USD, 10 days are billable: 10 × 2 = 20 USD.
Two details often cause disputes:
- Free days belong to each container. Containers picked up on different dates do not run out of free days on the same day.
- Partial invoices must carry the free days over. If a long rental is invoiced month by month, the free days are used up first and only the days beyond them are billed, so the total is the same as a single invoice.
Billing rules in the United States
The US Federal Maritime Commission (FMC) adopted a final rule on demurrage and detention billing, published on 26 February 2024 (89 Fed. Reg. 14330, 46 CFR Part 541) and effective on 28 May 2024, with two provisions delayed. Its main points:
- An invoice must be issued within 30 days of the date the charge was last incurred; otherwise the billed party does not have to pay it.
- The billed party has 30 days to contest the charges, and the billing party must try to resolve the dispute within 30 days after it is contested.
- Invoices may only be sent to the consignee or to the person who contracted for the transport or storage of the cargo.
- An invoice that does not contain the required information does not have to be paid.
Outside the US, demurrage and detention are set by each carrier's tariff and the contract, and local rules differ by country.
How to keep these charges under control
- Record the real gate-out and gate-in dates of every container, not the planned ones.
- Keep the free days and the rate of each contract next to the containers it covers.
- Check every day which containers are close to the end of their free time.
- Invoice (or check incoming invoices) container by container, with the days counted the same way as in the contract.
In Krak Stack, pickups and drop-offs are recorded on each container of a lease, the free days are counted container by container from the pickup day, and the per diem invoice lists only the days beyond the free days, period after period. See Leasing and per diem and the guide Free days and per diem in container leasing.
Frequently asked questions
Is detention the same as demurrage?
No. Demurrage covers the time a container stays inside the terminal after its free time; detention covers the time it stays outside the terminal before the empty container is returned.
Is per diem the same as detention?
In US shipping and trucking, per diem is usually another word for detention. In container leasing, per diem is the daily rental rate of a leased container.
Who pays demurrage and detention?
Usually the party that controls the cargo at that stage: the consignee for an import, the shipper for an export, as set out in the contract and the bill of lading terms.
Do weekends and public holidays count?
It depends on the tariff. Many carriers count calendar days, some exclude weekends or holidays from the free time. Check the tariff of the carrier or the terms of the lease.
What is "surestaries"?
"Surestaries" is the French word for demurrage. Detention is usually called "frais de détention" or "location" of the container.
Sources
- HFW, "FMC's New Demurrage and Detention Regulations Become Effective May 2024": https://www.hfw.com/insights/fmcs-new-demurrage-and-detention-regulations-become-effective-may-2024
- US Federal Maritime Commission, 46 CFR Part 541, Demurrage and Detention Billing Requirements (89 Fed. Reg. 14330, 26 February 2024).