Demurrage and detention are two clocks.
They start on different events, they stop on different events, and they are owed to two different companies. A screen that keeps one free-time number per container has to be wrong about one of them.
Demurrage runs while the box is still on the terminal. Detention runs while the box is held off it. The board counts both against the same container, names the counterparty on each row, and audits the carrier’s own invoice when it arrives.
Every row says which clock, and who is on the other end.
This is not a list of containers with a number of days beside them. Each row names the clock, the event that started it, the day free time ran out, and the company the money is owed to — because those four things differ between the two, and the phone call differs with them.
| Container | Clock | Started | Last free day | Over | Accrued |
|---|---|---|---|---|---|
| MSKU701235440HC · USLAX | DemurrageTerminal | Discharged 08/08 | 08/13 | 19USD 185/day | 3,515.00 |
| TCNU441906340HC · USLAX | DemurrageTerminal | Discharged 08/11 | 08/16 | 3Stopped — released 08/19 | 555.00 |
| TCNU4419063the same box | DetentionCarrier — HMM | Out-gated 08/19 | 08/23 | 9USD 125/day | 1,125.00 |
| MSDU228051440HC · export | DetentionCarrier — Maersk | Out-gated 08/21 | 08/25 | 7ERD 09/04 — cannot be returned yet | 875.00 |
Different events, different people.
Demurrage runs while the container is on the terminal. It starts when discharge begins, it stops when the box goes out of the gate, and it is owed to the terminal. Detention runs while the box is held outside. It starts at that same out-gate, it stops when the equipment is handed back, and it is owed to the carrier.
One event ends the first clock and begins the second, which is exactly why they cannot be one running total. TCNU4419063 appears twice above for that reason: three days of demurrage that have stopped, and nine days of detention that have not.
There is therefore no column here called free time. There is a clock, an event, a date and a counterparty, and the row is legible without anyone remembering which kind of box this was.
The carrier’s invoice is checked against the rule that governs it.
A demurrage or detention invoice has to carry certain information: twenty items of it, set out in 46 CFR §541.6. The audit reads the invoice against all twenty, counts the days in §541.7 as dates, and writes the letter if items are missing.
It reads the direction first.
The twenty items are not all required on every invoice. An import invoice has to carry the port of discharge. An export invoice has to carry the earliest return date and is not asked for a port of discharge at all. Checking every item against every invoice manufactures failures that are not failures, and one of those inside a letter is worse than sending no letter.
The thirty days are counted, not remembered.
§541.7 gives the billing party thirty days from the last day a charge was incurred to issue the invoice. This one charged up to 5 May and was issued on 17 June, which is forty-three days later and thirteen past the deadline. The same section gives the billed party thirty days from the invoice to ask for mitigation — a window that opened on 17 June and closed on 17 July. Today is 2 September, so the screen says the window is closed rather than leaving it to be worked out from an invoice date.
Why the letter is worth writing
§541.5 is direct about what a missing item does: failure to include the required information “eliminates any obligation … to pay.” That is the sentence the letter rests on, and it is the reason the eight items are listed by name with their clause beside them instead of being summarised as a score.
Free time — 02 September, then D&D invoice — HDMU-DD-040175, demo company- Open the free time board. Three rows accruing, running total USD 5,515.00.
- Point at TCNU4419063 on both of its rows: demurrage stopped, detention still running.
- Open the D&D invoice and run the audit, then stop on the eight missing items with their clauses beside them.
The two clocks never share a field.
It would be simpler to keep one free-time number per container and let the screen work out which kind it is. AMC did not, because there is no direction that single field can point in that is right.
With the field pointed at demurrage
The box already pulled goes quiet. Detention began at the out-gate, it is owed to the carrier rather than the terminal, and it is running at a different rate — but the number on the screen stopped moving on the day the second cost started. The screen goes calm at the moment the exposure begins.
With the field pointed at detention
The box still sitting on the terminal is then counted against the wrong company at the wrong rate, and the demurrage in fact accruing has no line at all. Whichever way the single field is pointed, one of the two clocks disappears — and it disappears quietly, which is the part that costs money.
And one clause the audit does not cite.
The audit compares an invoice against twenty items in §541.6, and not one of the twenty comes from §541.4. That is deliberate, and the reason is worth knowing before the letter is relied on.
§541.4 was vacated
On 23 September 2025 the Court of Appeals for the D.C. Circuit vacated 46 CFR §541.4. It is not in force. An argument built on it is an argument a carrier can dismiss in a single line, and software that still checks against it is quietly producing findings that cannot be defended.
The letter therefore never relies on it
The twenty items and the thirty days sit in §541.6 and §541.7, which stand. A dispute letter that cites a vacated clause tells the person reading it that nobody checked, and the rest of the letter is then read in that light. The clause on each row exists so that the rule can be read at source, which only helps if the rule is still there.
Stated plainly, before the demonstration.
A D&D invoice already paid, audited on the call.
The invoice is run against the twenty items of §541.6 during the call, the thirty days of §541.7 are counted from the last day charged, and the letter is printed with the clauses on it. If the invoice is clean, the demonstration says so.