Control time-based freight charges by separating the asset, location, clock, rate source, evidence, and party that could actually move the freight.

Detention, demurrage, per diem, and storage are often grouped as “accessorials” and sent to accounts payable as though they were variants of the same fee. They are not.

One can measure a driver waiting at a dock. Another can measure a container occupying terminal space. Another can measure equipment held outside a terminal. Rail demurrage concerns a railcar. Storage can arise under a terminal schedule, warehouse agreement, or another facility's rules. The names also vary by mode and contract.

The reliable distinction is not the invoice label. It is the clock:

Identify the asset or space being consumed, where it was, the event that started free time, the event that stopped the charge, the governing rate source, and the party that had a practical ability to act.

That six-field record turns an emotional dispute into an auditable one.

Detention vs. demurrage vs. per diem: the operating map

Charge in ordinary use What is being tied up Typical location Common governing source
Truck detention Driver, tractor, and often trailer time Shipper or receiver facility Shipper-carrier or broker-carrier contract, rate confirmation, carrier rules
Ocean demurrage Terminal space and an import or export container Marine terminal Ocean-carrier tariff or service contract, MTO schedule, Shipping Act and FMC rules
Ocean detention or container per diem Ocean container use Outside the marine terminal Ocean-carrier tariff, service contract, equipment terms, FMC rules
Chassis per diem or rental Chassis use During the equipment-interchange period Chassis-provider agreement or UIIA equipment-provider addendum
Rail demurrage Railcar and network capacity Customer, interchange, or serving-railroad context Rail contract or serving-carrier tariff, Surface Transportation Board rules
Storage Occupied facility space Terminal, rail facility, warehouse, yard, or third-party depot Facility tariff, schedule, warehouse agreement, or service contract

These are working descriptions, not universal legal definitions. The Federal Maritime Commission's rule deliberately defines ocean “demurrage or detention” broadly to include charges called per diem when they are assessed by covered ocean entities for marine-terminal space or shipping-container use. The current text of 46 CFR Part 541 controls the federal ocean-invoice analysis, not a company's preferred terminology.

Truck detention: a commercial clock with an operational owner

Truck detention usually begins when loading or unloading consumes more time than the agreed allowance. The allowance is frequently two hours in truckload practice, but two hours is not a universal federal entitlement or cutoff. It must come from the governing rate confirmation, contract, carrier rule, or other agreement.

Define six events before the load moves:

  1. appointment time;
  2. arrival at the facility or geofence;
  3. gate check-in or acceptance into the queue;
  4. dock assignment;
  5. loading or unloading completion;
  6. release and gate-out.

The parties must also decide which event starts compensable time. A truck can arrive early, wait off property, enter a security queue, and reach a dock much later. A facility can mark the appointment “on time” while the driver's electronic log shows hours consumed. Without an agreed clock, both records can be accurate and the invoice still disputed.

The FMCSA's current detention-time research program treats loading and unloading delay as an operating and safety problem, but it does not create a standard commercial fee. Procurement owns the contract. The facility owns door and labor readiness. Dispatch owns arrival communication. The driver or carrier owns contemporaneous timestamps. Freight audit owns the match between evidence and rate.

A workable truck-detention clause

The clause should state:

  • free-time allowance;
  • start and stop events;
  • treatment of early and late arrivals;
  • grace period and billing increments;
  • hourly rate and daily cap, if any;
  • who must sign or electronically verify time;
  • evidence accepted if the facility refuses to sign;
  • notice deadline and invoice deadline;
  • exclusions, such as carrier-caused delay;
  • treatment of lumper time, rejected product, restacking, or driver-assist work.

Detention should not become a substitute for another service. If the receiver asks the driver to sort, segregate, restack, or assist with unloading, identify whether that is included, separately priced, or prohibited. Time and labor are different cost objects even when they occur together.

Ocean demurrage: start with availability, free time, and the responsible party

For a conventional import move, ocean demurrage is associated with a container remaining at the marine terminal after allowed free time. The simple explanation breaks down quickly because “discharged from vessel” and “available for pickup” are not always the same event.

Availability can be affected by:

  • terminal discharge and grounding;
  • freight or documentation holds;
  • customs or other government holds;
  • terminal appointments;
  • delivery-order status;
  • chassis or equipment availability;
  • terminal closures and restricted receiving;
  • the last free day calculation in the applicable tariff or contract.

The operator's file should preserve each event rather than one screenshot of the final balance. The invoice may need to identify container availability, allowed free time, its start and end, and the specific charged dates under 46 CFR § 541.6. The process owner still needs source evidence: terminal availability messages, holds and releases, appointment attempts, gate transactions, and carrier notices.

The FMC's reasonableness framework centers on whether a practice serves a freight-fluidity incentive. 46 CFR § 545.5 lists nonexclusive considerations, including cargo availability, empty-container return, notice, and dispute practices. This does not mean every operational obstacle automatically cancels every charge. It means the reason for the delay, ability to act, applicable rule, and evidence matter.

For a deeper physical handoff, pair this analysis with the UniteCargo drayage operating guide.

Container detention and per diem: the equipment has left, but the clock has not

In common ocean practice, detention or per diem often measures the period after an import container leaves the terminal until the empty is returned to an authorized location. For exports, equipment-use clocks can run under a different sequence. The tariff, service contract, and equipment instructions control.

The return is not adequately documented by “driver tried.” Preserve:

  • interchange-out event;
  • container and chassis numbers;
  • free-time basis and calculated last free day;
  • empty-return instructions in effect for each attempted day;
  • earliest return date for exports, where applicable;
  • appointment searches and screenshots with timestamps;
  • terminal or depot closures;
  • rejection messages and reason codes;
  • dual-transaction requirements;
  • street-turn authorization;
  • final interchange receipt.

A return instruction can change while the box is in use. Assign one owner—usually the drayage dispatcher or import operations coordinator—to capture the instruction each day and send changes through a controlled channel. The driver should not be expected to resolve conflicting carrier portals at the gate.

Chassis per diem is a separate clock

The chassis may belong to a pool or equipment provider different from the container owner. Its rental or per-diem clock can therefore start and stop on different events from container detention.

For participants, the Uniform Intermodal Interchange and Facilities Access Agreement and provider-specific addenda can govern equipment use and disputes. IANA's UIIA program information notes that its arbitration process covers per diem, maintenance-and-repair, and equipment rental or use disputes after the applicable dispute processes are exhausted.

Accounts payable should never combine container and chassis charges into one “per diem” line without retaining both equipment numbers, providers, interchange records, and rate sources.

Storage: determine who owns the space and who issued the rule

“Storage” can describe several different charges:

  • marine-terminal storage for cargo or a container occupying terminal space;
  • rail-terminal or depot storage;
  • a transload or warehouse charge for freight held beyond agreed free days;
  • yard storage for a trailer, container, or loose freight;
  • storage after cargo rejection, customs activity, or failed delivery.

Do not assume that calling a charge storage places it outside ocean demurrage-and-detention regulation. Under 46 CFR Part 541, the issuer and substance of a charge matter: the rule covers invoices from ocean common carriers, marine terminal operators, and NVOCCs for covered terminal-space or container-use charges. Conversely, an independent warehouse's storage bill is not transformed into an FMC matter merely because the freight arrived in an ocean container.

The audit record should identify:

  • legal billing entity;
  • facility and space occupied;
  • cargo or equipment identifier;
  • governing tariff, terminal schedule, warehouse receipt, or contract;
  • free days and calendar convention;
  • rate tiers;
  • start and release events;
  • holds and disposition instructions;
  • tax, handling, out-gate, or administrative charges that are distinct from storage.

This distinction also prevents double counting. Two charges can overlap in calendar time and still price different resources, such as terminal space and ocean equipment. The right question is not “Were we billed twice?” but “What did each party provide, and does each governing document authorize this charge for these dates?”

Rail demurrage has its own federal framework

Rail demurrage is not ocean demurrage with a rail label. Under 49 CFR Part 1333, it is a charge that compensates for railcars held beyond free time and encourages efficient use of cars and the network. A serving carrier and its customer may contract; absent a contract, the serving carrier's demurrage tariff generally governs.

The rules address who may be liable and require actual notice of the tariff in stated circumstances. They also impose invoice-information requirements on Class I railroads. A rail customer should retain car initials and number, placement and release events, actual and constructive placement records, order and release messages, switching service records, bunching evidence, tariff version, credits, and the invoice calculation.

Do not send rail demurrage to the ocean-accessorial owner merely because both involve free time. The operations data, governing regulator, and tariff mechanics differ.

The ocean-invoice compliance check

As reviewed July 27, 2026, 46 CFR Part 541 requires covered ocean demurrage or detention invoices to contain specified identifying, timing, rate, dispute, and certification information. Material checks include:

  • bill of lading and container number;
  • port of discharge for imports;
  • why the billed party is the proper party;
  • invoice and due dates;
  • allowed free time, its start and end, and specific charged dates;
  • container availability for imports or earliest return date for exports;
  • applicable tariff, terminal schedule, service-contract, or negotiated rule;
  • rate or rates;
  • dispute contact, process, required documents, and timeframes;
  • certifications regarding FMC-rule consistency and billing-party contribution.

Failure to include required minimum information eliminates the billed party's obligation to pay the applicable charge under § 541.5. Treat that as a legal compliance check, not a reason to ignore a timely invoice.

The same part establishes key clocks:

  • a covered billing party generally must issue the invoice within 30 calendar days after the charge was last incurred;
  • an NVOCC billing a charge it received generally has 30 calendar days from the received invoice's issuance date;
  • the billing party must allow at least 30 calendar days from invoice issuance for a mitigation, refund, or waiver request;
  • the billing party must attempt to resolve a timely request within 30 calendar days after receipt, unless both parties agree to a later date.

One current-law caveat matters. In September 2025, the D.C. Circuit set aside 46 CFR § 541.4—the section that prescribed who could receive a demurrage or detention invoice—while leaving the rest of Part 541 in place. The FMC's notice on the decision confirms that status and says the Commission may revisit the subject in a future rulemaking.

The former § 541.4 billed-party restriction, including its simultaneous-invoice provision, should therefore not be treated as a current Part 541 requirement. Section 541.6 still requires the invoice to explain why the recipient is the proper party, and separate Shipping Act, tariff, bill-of-lading, and contract questions can still determine whether a charge is lawful or collectible. Do not read the vacatur as permission to invoice any entity connected to the freight.

Build an accessorial control tower without buying a “control tower”

The work requires ownership more than software.

Before arrival

  • Procurement: archive free-time rules, rates, dispute clocks, and incorporated tariffs.
  • Import or shipment operations: clear documents, releases, holds, appointments, and delivery instructions.
  • Facility owner: reserve labor, door, staging space, and receiving capacity.
  • Carrier or drayage dispatch: confirm driver, equipment, appointment, and communication route.
  • Finance: establish charge codes by clock, not one generic accessorial code.

While the clock is exposed

  • capture event timestamps from source systems;
  • record failed appointments and return attempts as they happen;
  • escalate holds to a named owner;
  • forecast last free day and projected charge daily;
  • compare mitigation cost—pre-pull, storage, alternate depot, drop, or extra shift—with expected exposure;
  • preserve instructions before a portal overwrites them.

At invoice

Run four tests:

  1. Identity: correct shipment, container, chassis, railcar, trailer, facility, and billed party?
  2. Time: correct availability, free time, charged days, calendar, and stop event?
  3. Authority: correct contract, tariff, schedule, addendum, and rate version?
  4. Causation and control: what prevented movement, who could act, what evidence supports mitigation or dispute?

If the ocean carrier's charge may violate the Shipping Act, the FMC provides a Charge Complaint process. The Commission asks for the carrier identity, explanation, and documents such as invoices, bills of lading, proof of payment, denied-appointment screenshots, gate closures, and relevant emails. Preserve that package during the event, not after the portal history disappears.

A weekly scorecard that changes behavior

Track more than dollars paid:

  • exposed shipments by last free day;
  • charges incurred by clock type;
  • avoidable versus disputed versus contractually expected amounts;
  • root cause and operational owner;
  • percentage supported by complete event evidence;
  • disputes filed within the governing period;
  • recoveries and waived amounts;
  • repeat facilities, carriers, customers, and lanes;
  • dwell eliminated through process change.

“Accessorial spend went down” is not enough. Spend can fall because volume fell or invoices arrived late. A credible result connects a specific control—earlier customs release, an extra receiving shift, pre-pull authorization, better appointment capture—to fewer exposed hours or days.

The operating takeaway

Time-based charges stop looking random when the operation can answer:

  • Which asset or space was unavailable to someone else?
  • What event started and stopped the charge?
  • Which free-time and rate rule applied?
  • Who received notice and who could act?
  • What evidence was captured before the invoice?

Build those answers into the shipment record. The dispute process then becomes the last control, not the first time anyone reconstructs what happened.

This article provides operational education, not legal advice. Ocean, rail, motor-carrier, equipment, terminal, and warehouse charges arise under different contracts and legal regimes; obtain qualified advice for a specific dispute.

Sources and further reading

Logistics