Demurrage Is a Causality Problem, Not a Rate Check

A demurrage invoice lands for six days on one container. Someone checks the per diem against the tariff, finds that it matches, and releases the payment.

That check tested the smallest number on the document. Demurrage is priced by the day, so the amount is a count multiplied by a rate, and the count carries all of the risk. Underneath the count sits a claim nobody verified: that each of those six days was yours.

Recompute the count before you argue about the rate

The invoice tells you when free time started and when it ran out. Under 46 CFR 541.6 it has to: the allowed free time in days, its start and end dates, the container availability date on imports, the earliest return date on exports, and the specific dates charged.

Those fields are the billing party's own arithmetic, not an independent record. Rebuild the number from events instead. Discharge, the terminal's availability flag, gate out, gate in and empty return each carry a timestamp held by the terminal or a visibility provider. Then apply the exclusions the governing document actually grants, which is where the two versions separate. A carrier clause counting calendar days and a terminal schedule that skips Sundays and observed holidays will not arrive at the same six.

Dwell figures show how little margin there is for an error of one. The Pacific Merchant Shipping Association reported August 2026 container dwell at Los Angeles and Long Beach of 2.95 days for boxes leaving by truck and 6.75 days for rail-bound boxes, the latter up from 6.34 days in July. Those containers sit in the same yard under the same free time and land on opposite sides of it, because what holds a rail container is railroad capacity rather than any decision the consignee made.

Every billed day has an author

Once the count is right, the second question is who caused each day inside it. Treating the invoice as a single object destroys that question, because a six-day charge is often four unrelated stories stacked on one container number.

Only the last row is a day you owe without an argument.

An exam is the cleanest case. Customs selects the container, it travels to an examination station, and it comes back some days later. Nothing in that sequence was a choice you made, and the tariff clock keeps running throughout.

A freight hold is the awkward one, because the party that placed it is frequently the party invoicing you. Section 541.6 requires the billing party to state on the invoice that its own performance did not cause or contribute to the charge. A carrier that held the container over a documentation question and then billed the storage has signed that line anyway.

A buried box announces nothing. The terminal sets the availability flag, your drayman books the appointment, and the container is under three others the yard cannot work that shift. The availability date printed on the invoice says it was yours to collect. The appointment record says it was not.

The empty return is where the charge turns into detention and where tariff logic breaks most visibly. A full depot, an appointment system with nothing open, or a carrier insisting on a dual transaction all generate days the consignee cannot shorten by trying harder.

The Commission already treats this as a causality question

Attribution is not an inventive dispute tactic. It is the test the regulator wrote down. Under 46 CFR 545.5 the Commission judges whether a demurrage or detention charge is reasonable by considering how far it serves its intended purpose as a financial incentive to keep cargo and equipment moving. The same rule names government inspections as a factor, and states that detention imposed where it cannot serve that incentive purpose, with empty containers that cannot be returned given as the example, is likely to be found unreasonable absent extenuating circumstances.

A federal appeals court has now backed that reading. In Evergreen Shipping Agency (America) Corp. v. Federal Maritime Commission, decided April 28, 2026, the D.C. Circuit denied the carrier's petition and left the Commission's finding in place: detention billed for May 23 to 25, 2020, when the Port of Savannah was closed and the receiving plant was shut, was unreasonable. The court held that freight fluidity has always been integral to the incentive principle. The sum at stake across those three days was $510.

The burden runs in your favour too. Under 46 U.S.C. 41310 a carrier facing a charge complaint bears the burden of establishing that its demurrage or detention charges were reasonable. The Commission's charge complaint procedures rule, published on September 1, 2026, confirms that the same shift applies whether the complaint arrives through the interim email process or the traditional procedures. You do not have to prove the day was not yours. The carrier has to prove that it was.

None of that helps if you cannot describe what happened to the container. A complaint saying the charge looks excessive starts a conversation. A complaint naming the exam date, the hold window and the three days the depot turned the empty away ends in a refund.

The evidence exists and never reaches the audit

Nothing above needs data you do not already hold. The exam notice is with your broker. Availability and gate events are in the visibility feed. The hold is in the carrier portal. The refused appointment is in the drayman's system. The invoice is in accounts payable.

Five sources, five owners, and a window that shuts quickly. 46 CFR 541.7 gives the billing party 30 calendar days from the last day charged to issue the invoice, and the dispute timeframes it has to publish under 541.6 run from there. Pulling five systems together by hand, per container, inside that window is the step that quietly does not happen, so the charge gets approved on trust.

What Penny does with a demurrage line

Penny rebuilds the day count from events before she looks at the invoice total, then assigns a cause to each day that survives the recount. Days traceable to an exam, a carrier hold, an unworkable stack or a refused empty leave the charge with the supporting document already attached, which is the shape a dispute needs in order to survive a rebuttal.

Chase supplies the execution trail the count rests on: the availability flag, the gate events, the appointment history. Our post on why road audit logic collapses on containers explains why the two agents are hard to separate on ocean work.

Where to start this quarter

Pull twenty import containers your team paid demurrage on. Write the billed days down the page for each one, then put a cause and a document against every day. Stop when you run out of evidence rather than guessing.

The days you cannot attribute are the measure of the problem. They are also the days a carrier would have had to justify, and did not, because nobody asked.

Book a walkthrough to see Penny recount and attribute the demurrage days on your own container invoices.