# Demurrage vs detention: the difference, per diem, storage, wharfage

Demurrage is time-based rent on cargo or a container sitting in a terminal after free time; detention is time-based rent on a container used outside the terminal. The Federal Maritime Commission defines both together, and its rules apply whichever word the invoice uses. Storage, wharfage and quay rent are different charges.


## The six terms side by side

| Term | Who charges it | What it is for | When the clock runs | Who is billed |
|---|---|---|---|---|
| **Demurrage** | An ocean carrier, a marine terminal operator, or a non-vessel-operating common carrier (46 CFR 541.2) | Use of marine terminal space, in practice cargo or a full container left in the terminal | After free time ends; the carrier or terminal tariff says when free time starts | The "billed party" named on the invoice |
| **Detention** | The same parties | Use of the shipping container, in practice a container taken out of the terminal and not returned in time | In the tariffs we read (ONE, Hapag-Lloyd, ZIM) from gate-out or interchange, after its own free time | The "billed party" named on the invoice |
| **Per diem** | The same parties | A daily charge. The FMC definition includes per diem charges inside "demurrage or detention" | Per the tariff the invoice cites | The "billed party" |
| **Storage** (terminal storage) | A marine terminal operator, under its terminal schedule (46 CFR 525.1) | The service of providing warehouse or terminal facilities for inbound or outbound cargo after free time expires | After free time under the terminal schedule | As the terminal schedule provides |
| **Wharfage** | A marine terminal operator | A charge on cargo passing over, onto or under a wharf. The federal definition says it is solely the charge for use of a wharf | No daily clock: a charge per movement of the cargo | The cargo or the vessel |
| **Quay rent** | Not defined in the US federal rules | Not a term in 46 CFR; we searched the eCFR on 2026-10-21 and found no use of it | Ask which tariff rule the charge is based on | Ask the issuer |

The "wharf demurrage" of a terminal schedule is the port's own version of demurrage: 46 CFR 525.1(c)(23) defines it as a charge assessed against cargo remaining in or on terminal facilities after the expiration of free time, unless arrangements have been made for storage. Free time, in the same section, is the period in the terminal schedule during which cargo may stay on terminal property free of wharf demurrage or terminal storage charges.

## What the FMC definition says

46 CFR 541.3 defines "demurrage or detention" as "any charges, including 'per diem' charges, assessed by ocean common carriers, marine terminal operators, or non-vessel-operating common carriers related to the use of marine terminal space (e.g., land) or shipping containers, but not including freight charges." The D.C. Circuit described the two as charges that arise when there is unduly prolonged use of shipping containers or of space in a marine terminal ([World Shipping Council v. FMC, 2025](https://media.cadc.uscourts.gov/opinions/docs/2025/09/24-1088-2136451.pdf)). The rule does not draw a line between the two words, so we do not either: look at what the invoice says it charges for, and at the tariff rule it cites.

## Why the word on the invoice matters

- **The rule behind the rate.** 46 CFR 541.6(c)(2) requires the invoice to name the applicable detention or demurrage rule on which the daily rate is based, for example the tariff name and rule number. A charge called "per diem" or "storage" still has to cite one. See [what a US invoice must show](/en/fmc/).
- **Reasonableness.** The FMC's interpretive rule, 46 CFR 545.5(c), says it looks at whether the charge serves its purpose as a financial incentive. It adds that, absent extenuating circumstances, detention charged when empty containers cannot be returned is likely to be found unreasonable.
- **Which tariff applies.** A carrier's demurrage and detention tariff and a port's terminal schedule are different documents. Port tariffs have their own sections for wharfage, free time, demurrage and storage; for example, the Port of Los Angeles lists Wharfage (Section 5) and Free Time, Demurrage, and Storage (Section 7) in [Tariff No. 4](https://www.portoflosangeles.org/business/tariff). We do not copy port or carrier rates; our pages link to them.

## Check your own invoice

1. Find the charge name, the dates charged and the rule it cites.
2. Work out the [last free day](/en/demurrage/last-free-day/) from the discharge date and the free time in the tariff.
3. Check who the invoice says is liable: [who pays demurrage and detention](/en/demurrage/who-pays/).
4. If something is missing or wrong, [draft the letter](/en/demurrage/letter/), then see the [FMC process](/en/fmc/).

{{< carrier-links kind="us" label="Carrier pages" >}}

{{< linkrow label="Port pages" >}}
[Los Angeles and Long Beach](/en/demurrage/los-angeles-long-beach/)
[New York and New Jersey](/en/demurrage/new-york-new-jersey/)
[Houston](/en/demurrage/houston/)
[Savannah](/en/demurrage/savannah/)
{{< /linkrow >}}

Rail storage is a separate set of rules: [rail intermodal storage](/en/demurrage/rail/).


## FAQ

**Is demurrage the same as detention?**

No, but the FMC treats them under one definition: charges for the use of marine terminal space or shipping containers, not freight. Demurrage is usually the terminal-space side, detention the container side. The same invoice rules in 46 CFR 541.6 apply to both.

**Is per diem the same as detention?**

The FMC definition in 46 CFR 541.3 says demurrage or detention includes any charges 'including per diem charges'. A per diem on a container is therefore covered by the same rules, whatever the invoice calls it.

**Who pays demurrage, the importer or the exporter?**

The party the invoice is addressed to and that the invoice shows to be liable. That depends on the bill of lading and the carrier's terms, not on the sale terms. See who pays demurrage and detention.

**Do I pay wharfage on top of demurrage?**

They are separate charges. Wharfage is a charge on cargo passing over a wharf, with no daily clock; demurrage and detention accrue per day after free time.


## Sources

- [46 CFR 541.3, Definitions (eCFR)](https://www.ecfr.gov/current/title-46/section-541.3)
- [46 CFR 525.1, Purpose and scope, definitions (eCFR)](https://www.ecfr.gov/current/title-46/section-525.1)
- [46 CFR 545.5, Unjust and unreasonable practices with respect to demurrage and detention (eCFR)](https://www.ecfr.gov/current/title-46/section-545.5)
- [World Shipping Council v. FMC, No. 24-1088 (D.C. Cir. Sept. 23, 2025)](https://media.cadc.uscourts.gov/opinions/docs/2025/09/24-1088-2136451.pdf)
- [Port of Los Angeles Tariff No. 4](https://www.portoflosangeles.org/business/tariff)

Canonical: https://purserhouse.com/en/demurrage/vs/