Demurrage vs per diem vs detention in drayage

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?

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, fully in effect since May 28, 2024, 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 (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.

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, the free-time clock shows this kind of cost per container, already charged and by Friday, and the demurrage calculator 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:

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 sets the timing:

One section has changed. In World Shipping Council v. FMC, 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 (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 follows a booking from cutoff to the last free day, where these clocks begin.