# Demurrage vs per diem vs detention in drayage

> Who charges demurrage, per diem and detention on a container, when each clock starts and stops, and a worked import example with every charge computed.

URL: https://roadmark.ai/blog/demurrage-per-diem-detention
Language: en
Last updated: 2026-09-15

**TL;DR:** Demurrage is charged while a full import container sits at the terminal past its free time; per diem, which ocean carriers also call detention, is charged while the container is outside the terminal past its free time, until the empty is returned. Truck detention is what the drayage carrier bills when its driver waits at a dock. Each has its own clock, billing party and free time, set by the carrier's or terminal's tariff, the UIIA addendum and your rate agreement.

Three different charges land on a drayage move, and they run on three different clocks. **Demurrage** runs while the full container sits at the terminal. **Per diem** (the ocean carrier's container detention) runs while the box is out of the terminal, until the empty goes back. **Truck detention** is the drayage carrier's own charge for its driver waiting at a dock. Mixing them up is how the wrong party gets billed, or nobody does.

## Who charges what, and when does each clock run?

| Charge                 | Who bills whom                                                              | The clock runs                                                                                           | Terms set by                                          |
| ---------------------- | --------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------- | ----------------------------------------------------- |
| Demurrage              | Ocean carrier (or the terminal, as storage) bills the importer or consignee | From the end of free time, counted from discharge or availability, until the full container is out-gated | Carrier tariff or service contract, terminal schedule |
| Per diem, or detention | Ocean carrier bills the trucker under the UIIA, or the shipper              | From the end of free time, counted from out-gate, until the empty is returned                            | UIIA addendum, carrier tariff                         |
| Chassis usage          | Chassis pool or provider bills the trucker, or the importer                 | From chassis out-gate to its return, often with no free days                                             | Pool or provider rates                                |
| Truck detention        | Drayage carrier bills its customer                                          | From the end of free time at the dock until the driver is released                                       | Drayage rate agreement                                |

Some carriers merge demurrage and detention into one combined free-time allowance, and rail ramps charge their own storage. Read the specific tariff for each port, ramp and carrier: free days, tiers and whether weekends count all vary.

## When does the demurrage clock start?

Free time usually starts on the day the container is discharged or made available at the terminal, depending on the tariff. The last free day (LFD) is the date that matters for dispatch: after it, demurrage runs for each day, or part of a day, until the full container leaves the terminal.

In U.S. trades, the invoice has to show the arithmetic. The Federal Maritime Commission's [billing rule](https://www.ecfr.gov/current/title-46/chapter-IV/subchapter-B/part-541), fully in effect since [May 28, 2024](https://www.fmc.gov/articles/final-rule-on-demurrage-detention-cleared-to-take-full-effect-may-28/), requires every demurrage or detention invoice to include the free time in days, its start and end dates, the availability date for imports, the dates charged, the tariff rule or contract behind the rate, and a contact for disputes. An invoice missing required information "eliminates any obligation of the billed party to pay."

## Per diem or detention: what's the difference?

Mostly the name and who pays. The [Uniform Intermodal Interchange Agreement](https://uiia.intermodal.org/documents/uiia/newuiia-Home.pdf) (UIIA), which governs how truckers take ocean carriers' equipment, defines per diem as the charge for equipment not returned by the end of free time, "whether or not it is referred to as Per Diem, a detention charge, or otherwise." The FMC's rule also defines demurrage and detention to include "per diem" charges.

In practice, on a merchant-haulage move the ocean carrier bills per diem to the trucker who took the box out under the UIIA, and the trucker rebills its customer if the rate agreement says so. Some carriers bill the shipper or consignee directly and call it detention. Either way it's the same clock, and only one party should pay it.

The UIIA also sets deadlines that help truckers: the provider must invoice per diem within 60 calendar days of the equipment's return or lose the right to it, must supply evidence such as equipment interchange receipts, and the motor carrier must dispute in writing within 30 calendar days.

## What are truck detention and chassis charges on a drayage move?

**Truck detention** belongs to the drayage carrier: its driver waited past free time at the terminal or the customer's dock. Drayage rate agreements commonly give an hour or two free and bill in 15-minute increments after that. A driver held 2 h 10 m on a live unload with one hour free, billed in 15-minute increments rounded up, bills 1 h 15 m: at $85.00 an hour, that's 5 × $21.25 = $106.25. Amounts in this article are in US dollars.

**Chassis usage** is billed per day by the chassis pool or provider from out-gate to return, often with no free days. A box that sits at the customer for a week is also a chassis that sits there for a week.

## Worked example: what does one slow import cost?

An import 40-foot container, with illustrative rates. Your tariffs will differ; the method won't.

- Available at the terminal Monday, Sep 14, 2026. Four calendar days free, so the LFD is Thursday, Sep 17. Demurrage is $150.00 a day for the first four days, then $300.00.
- The consignee's DC can't take it until Tuesday, Sep 22. It's out-gated and dropped there on a pool chassis that day.
- Four calendar days of per diem free time from out-gate, then $125.00 a day. Chassis at $35.00 a day from out-gate.
- The consignee unloads slowly and the empty goes back Wednesday, Sep 30.

| Charge    | Chargeable days                         | Calculation               | Amount        |
| --------- | --------------------------------------- | ------------------------- | ------------- |
| Demurrage | Sep 18 to 22: 5 days                    | 4 × $150.00 + 1 × $300.00 | $900.00       |
| Per diem  | Free Sep 22 to 25; Sep 26 to 30: 5 days | 5 × $125.00               | $625.00       |
| Chassis   | Sep 22 to 30: 9 days                    | 9 × $35.00                | $315.00       |
| **Total** |                                         |                           | **$1,840.00** |

If the trucker pays the demurrage to get the box released, or is billed the per diem under the UIIA, it normally passes them to its customer at cost with the carrier's invoices attached, and rebills the chassis under the drayage agreement. On our [drayage page](https://roadmark.ai/drayage), the free-time clock shows this kind of cost per container, already charged and by Friday, and the [demurrage calculator](https://roadmark.ai/tools/demurrage) runs it for your own tiers.

## Would a pre-pull have been cheaper?

A pre-pull moves the box to the trucker's yard before the LFD, which stops demurrage but starts the per diem clock early. Same container, pulled on the LFD (Thursday, Sep 17), held in the yard at $50.00 a day for 5 days, with a $150.00 pre-pull charge:

| Charge       | Calculation                                   | Amount        |
| ------------ | --------------------------------------------- | ------------- |
| Demurrage    | Out on the LFD                                | $0.00         |
| Per diem     | Free Sep 17 to 20; Sep 21 to 30: 10 × $125.00 | $1,250.00     |
| Yard storage | 5 × $50.00                                    | $250.00       |
| Pre-pull     | Flat                                          | $150.00       |
| Chassis      | Sep 17 to 30: 14 × $35.00                     | $490.00       |
| **Total**    |                                               | **$2,140.00** |

Here the pre-pull costs $300.00 more, because the per diem free days were used up sitting in the yard. But each further day of waiting would cost $300.00 at the terminal against $210.00 in the yard ($125.00 per diem, $50.00 storage, $35.00 chassis). If the DC had pushed delivery back four or more days, the pre-pull would have come out ahead. Run both numbers on every box that's close to its LFD.

## What do U.S. rules say about billing demurrage and detention?

For ocean carriers, marine terminal operators and NVOCCs in U.S. trades, the FMC's rule at [46 CFR Part 541](https://www.ecfr.gov/current/title-46/chapter-IV/subchapter-B/part-541) sets the timing:

| Requirement                          | Rule                                                       |
| ------------------------------------ | ---------------------------------------------------------- |
| Invoice deadline                     | 30 calendar days from the day the charge was last incurred |
| NVOCC passing on a charge            | 30 calendar days from the invoice it received              |
| Window to request a waiver or refund | At least 30 calendar days from the invoice date            |
| Billing party's response             | Attempt to resolve within 30 calendar days of the request  |
| Late or incomplete invoice           | The billed party isn't required to pay                     |

One section has changed. In [World Shipping Council v. FMC](https://www.fmc.gov/articles/u-s-court-of-appeals-issues-decision-in-case-on-demurrage-and-detention-billing-practices/), decided September 23, 2025, the D.C. Circuit set aside section 541.4, which limited who could be sent an invoice. The rest of the rule, including the deadlines and the required contents, remains in effect.

Behind it sits the FMC's [incentive principle](https://www.federalregister.gov/documents/2020/05/18/2020-09370/interpretive-rule-on-demurrage-and-detention-under-the-shipping-act) (46 CFR 545.5): demurrage and detention exist to get containers moving, so charging them when a trucker or importer can't pick up or return a box is a sign the practice may be unreasonable. Record every day the terminal had no appointments or wouldn't take empties; that's the evidence for a waiver request.

These rules cover U.S. trades. At Canadian ports and rail ramps, the carrier's tariff and your contracts are what you dispute against, so keep the same records. Our [ocean freight page](https://roadmark.ai/ocean-freight) follows a booking from cutoff to the last free day, where these clocks begin.

## FAQ

### Is per diem the same as detention?

For the container itself, yes: it's the daily charge for keeping the ocean carrier's box outside the terminal past free time. The UIIA treats a charge as per diem whether or not it's called per diem or detention. The difference is usually who gets billed: per diem goes to the trucker under the UIIA, detention to the shipper or consignee.

### When does demurrage free time start?

It depends on the tariff: commonly on the day the container is discharged or made available at the terminal. The invoice has to show it. Under the FMC's billing rule, U.S. demurrage and detention invoices must state the free time, its start and end dates and, for imports, the availability date.

### How long does an ocean carrier have to send a demurrage or detention invoice?

For U.S. trades, 30 calendar days from the day the charge was last incurred under 46 CFR 541.7, or the billed party doesn't have to pay. Under the UIIA, equipment providers must invoice the motor carrier for per diem within 60 days of the equipment's return.

### Does a pre-pull always save money?

No. A pre-pull stops demurrage but starts the per diem clock early and adds yard storage and chassis days. It pays when demurrage has reached a high tier and delivery is still several days away. Run both numbers.

### Can I dispute demurrage when the terminal had no appointments?

In U.S. trades, that's what the FMC's incentive principle is for: charges are meant to get containers moving, so being billed when you couldn't retrieve or return the box is grounds to ask for a waiver. Request it within the window on the invoice, which must be at least 30 days.

## Related pages

- [Demurrage and per diem calculator](https://roadmark.ai/tools/demurrage): Last free day, charged days and the total for a container at the terminal or out on per diem, with tiered rates.
- [Drayage](https://roadmark.ai/drayage): Free time, per diem, chassis and port appointments
- [Ocean freight](https://roadmark.ai/ocean-freight): Containers, cutoffs and demurrage
- [Intermodal](https://roadmark.ai/intermodal): Ramps and rail cutoffs

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