A chassis per diem charge dispute almost never turns on the daily rate. It turns on which of three separate charges you are actually looking at. One container generates demurrage while it sits inside the terminal, container per diem (also called container detention) while it is out on the street past free time, and chassis per diem for every day someone holds the chassis under it. Three assets, three owners, three clocks, and they arrive on your desk as three invoices that all reference the same container number and overlapping dates.
Some of that overlap is legitimate. A container out on a chassis for four days genuinely incurs both container per diem and chassis per diem, because two different pieces of equipment are being held. Some of it is not: the same chassis billed by both the ocean carrier and the pool operator, or demurrage and container per diem billed for the same calendar day when the box can only have been in one place.
Sorting the legitimate overlap from the duplicate is the whole job. The method is a per-container timeline, and once you build one you will find you can settle most of these in about fifteen minutes.
The three charges, laid side by side
Start by getting the vocabulary exact, because the invoices will not help you. Carriers, terminals, and chassis providers use “detention” and “per diem” for different things, sometimes on the same page.
| Charge | What is being held | Where it is | Who typically bills | Clock ends when |
|---|---|---|---|---|
| Demurrage | The container and the terminal ground under it | Inside the terminal | Marine terminal operator or ocean carrier | The container leaves the terminal |
| Container per diem (container detention) | The container itself | Outside the terminal | Ocean carrier or NVOCC | The empty container is returned |
| Chassis per diem | The chassis | Wherever the chassis is | Chassis pool operator, equipment provider, ocean carrier, or the drayman as a pass-through | The chassis is returned to an approved location |
The distinction that resolves most disputes is the second column. Demurrage bills you for occupying terminal real estate. Container per diem bills you for keeping the box. Chassis per diem bills you for keeping the wheels. If two invoices claim the same day for the same asset, one of them is wrong. If two invoices claim the same day for different assets, both can be right.
The broader taxonomy across truckload and ocean, including where inland detention sits, is set out in detention versus demurrage versus per diem and who owes what.
Why the chassis gets billed separately at all
Chassis used to arrive bundled. The ocean carrier owned the equipment, supplied it with the container, and the cost sat inside the ocean freight. That model is largely gone at U.S. ports. Chassis are now supplied by pools and independent equipment providers, and the daily usage charge arrives as its own line, from its own party, on its own paper. That is what people mean by split billing.
Which party bills you depends on how the move was structured, and there are three common shapes.
The chassis provider bills the motor carrier, who passes it through. Your drayman pulls a chassis from a pool under an interchange agreement, gets billed for the usage days, and re-bills you on the drayage invoice. Audit question: does your drayage agreement permit a markup on pass-through equipment charges, and if so, how much? A pass-through line that quietly carries a percentage on top is a contract question, and it is one you can only answer by reading the agreement.
The ocean carrier bills you directly for chassis it supplied, often on the same invoice as container per diem. Audit question: are the two lines drawing from the same free time allowance or from different ones, and does the invoice say?
The pool or equipment provider bills you directly as the cargo interest. Audit question: are you a party to any agreement with that provider at all, or is the contractual chain actually provider to motor carrier?
None of those is improper. The problem is that a container moved under a mix of these can generate a chassis charge from two directions, and nobody in the chain has visibility into all of it except you.
Does the FMC billing rule reach chassis per diem?
Partly, and the boundary matters, so be careful with it.
46 CFR 541.3 defines demurrage or detention as any charges, including per diem charges, assessed by ocean common carriers, marine terminal operators, or non-vessel-operating common carriers related to the use of marine terminal space or shipping containers, but not including freight charges. Part 541 applies to invoices issued by those three kinds of party.
Two consequences follow.
A per diem charge from an ocean carrier, NVOCC, or terminal is squarely inside the rule. It has to carry every required field, it has to be issued within 30 calendar days of the last day the charge was incurred, and 46 CFR 541.5 says failure to include any required minimum information eliminates the obligation to pay. The full field list and the audit procedure are in what the FMC demurrage and detention billing rule requires on an invoice.
A chassis usage invoice from a pool operator or equipment provider that is none of those three parties sits outside the rule. The definition is written around terminal space and shipping containers, and the applicability section names ocean common carriers, marine terminal operators, and NVOCCs as the billing parties covered. An equipment leasing company billing you for chassis days is not obviously any of them. Where the rule does not reach, the charge is contractual, governed by the interchange or usage agreement and by whatever your drayage contract says about pass-throughs.
That is the honest reading, and the practical takeaway is that you should not open a chassis dispute by citing Part 541 without first identifying who issued the invoice. If it came from the ocean carrier, cite the rule. If it came from a chassis pool, cite the agreement. Getting that backwards is the fastest way to have your dispute dismissed on the first reply.
Build the container timeline
Everything resolves against one artifact: a single dated timeline per container, with each event sourced.
The events you need, in order:
- Vessel discharge date. From the arrival notice or the carrier’s tracking.
- Container availability date. When the box was actually released for pickup, after customs and terminal holds cleared. This is not the discharge date and the gap is often several days. On a compliant demurrage invoice this is a required field.
- Demurrage free time start and end. Required fields on the invoice under the FMC rule. If they are absent, you cannot check the charge and neither can the person who sent it.
- Out-gate date and time. When the container physically left the terminal. This is the boundary between demurrage and container per diem, and it is the single most useful timestamp in the whole file.
- Chassis out-gate or interchange-out. Often the same moment, but not always, especially where a chassis was flipped or swapped mid-move.
- Delivery and unload at your facility. The dwell you actually control.
- Empty return date and time. Ends container per diem.
- Chassis return or interchange-in. Ends chassis per diem. This can be days after the empty return if the chassis went back to a different location or sat in the drayman’s yard.
- Terminal closures, appointment unavailability, and holds for any day in the range.
Steps four, seven, and eight are the ones that settle disputes. Once you have the out-gate, the empty return, and the chassis interchange-in written down with sources, every charged day either falls inside a window you can account for or it does not.
The discipline here is the same one that makes an inland detention claim work when no gate system exists: pin the moments with records created automatically by systems with no stake in the outcome, then do the arithmetic in public. That method is in building a detention claim at a facility with no gate system.
The five overlaps worth checking
Run these against the timeline. They cover most of what an audit actually finds.
Demurrage and container per diem on the same day. The container cannot be inside the terminal and out on the street at once. Some overlap on the out-gate day itself is normal, since both charges are usually assessed in whole days. Overlap across two or more days points to a wrong out-gate date somewhere.
Chassis per diem billed twice. Once by the ocean carrier as part of a bundled equipment charge and again by the pool, or once directly to you and again through the drayman’s pass-through. Same asset, same days, two payers’ worth of invoices. The general pattern and how to catch it across statements is in how to detect a duplicate freight invoice, and under 49 CFR 378.2 a duplicate payment on the motor carrier side is defined simply as two or more payments for transporting the same shipment.
Chassis days running past the empty return. If the empty container went back Tuesday and the chassis invoice runs through Friday, ask where the chassis was Wednesday and Thursday. Sometimes the honest answer is that the return location would not accept the chassis, which is a real cost with a real cause. Sometimes it is that the drayman kept it for the next load.
Free time counted on different calendars. Container free time and chassis free time are frequently different allowances, and they may or may not exclude weekends and holidays. Two charges on one container can therefore start on different days legitimately. The invoice has to tell you which allowance applied.
Days when the terminal could not take the return. Closures, no available appointments, and equipment restrictions are the strongest mitigation argument you have on any per diem charge. They are also the argument that requires contemporaneous proof: the appointment system screenshot, the dated closure notice, the drayman’s rejected-return record. Collected after the fact, this evidence is nearly impossible to reconstruct.
What to ask for, and from whom
| Question | Ask | Document that answers it |
|---|---|---|
| When was the container actually available? | Ocean carrier | Availability date on the demurrage invoice, or terminal release record |
| When did the container out-gate? | Terminal or drayman | Terminal out-gate record, interchange receipt |
| When did the empty return? | Drayman | Empty in-gate receipt, equipment interchange receipt |
| When did the chassis come back? | Drayman or pool | Interchange-in record from the pool |
| Which rule sets this rate? | Whoever billed | Tariff name and rule number, or service contract section (a required field on covered invoices) |
| Was a return appointment available? | Drayman | Dated appointment system record, closure notice |
| Is a markup allowed on the pass-through? | Yourself | Your drayage agreement |
Ask for these in one message per container, not one message per invoice. A drayman who receives a single clear list will usually answer it. One who receives four separate emails about the same box over three weeks will not.
Where the clock puts pressure on you
Deadlines cut in both directions and they run quietly.
On the covered ocean-side charges, the billing party has 30 calendar days from the last day the charge was incurred to issue the invoice, and you get at least 30 calendar days from the invoice issuance date to request mitigation, refund, or waiver, with the billing party obliged to attempt to resolve within 30 days of receiving your request. That is the structure in 46 CFR 541.7 and 46 CFR 541.8.
On the motor carrier side of the same move, the drayage invoice is governed by the same clocks as any other truckload bill. Under 49 U.S.C. 13710 a carrier must bill charges beyond those originally billed within 180 days of your receipt of the original bill, and you must contest within 180 days of receipt to preserve your challenge. If you have already paid, 49 CFR 378.8 requires the processing carrier to pay, decline, or settle a written overcharge claim within 60 days of receipt absent a written agreement to extend. Those and the rest live in every freight billing deadline that can cost you money.
The practical risk is that a chassis pass-through appears on a drayage rebill months after the original invoice, by which time the interchange records are cold and the box is long gone. Screening rebills for late equipment charges is worth a standing rule in your AP workflow.
The checklist
- Identify who issued each invoice: ocean carrier, NVOCC, terminal, chassis provider, or drayman.
- Classify every line as demurrage, container per diem, or chassis per diem. Ignore the label on the invoice and use the asset being held.
- Build the container timeline with sourced dates for availability, out-gate, delivery, empty return, and chassis interchange-in.
- Check for demurrage and container per diem claiming the same days.
- Check for the same chassis days arriving from two directions.
- Check whether chassis days run past the empty return, and why.
- Confirm which free time allowance applied to each charge, and whether weekends and holidays were excluded.
- Pull contemporaneous evidence for any day the terminal could not accept a return.
- For ocean-carrier, NVOCC, and terminal invoices, run the FMC contents and 30-day issuance checks before arguing the arithmetic.
- For chassis pool and pass-through charges, argue from the interchange agreement and your drayage contract, not from the FMC rule.
Two habits do most of the work. Capture the out-gate and both return timestamps on every container while the move is live, the same way you would capture when detention free time starts on an inland load. And when an invoice fails a required-contents check, say which field is missing rather than that the invoice is unclear. Specificity is what turns an argument into a correction.
Sources
- 46 CFR 541.3, Definitions of demurrage or detention, billing party and billed party (Cornell LII)
- 46 CFR 541.5, Failure to include required information (Cornell LII)
- 46 CFR 541.6, Contents of invoice (Cornell LII)
- 46 CFR 541.7, Issuance of demurrage and detention invoices within 30 days (Cornell LII)
- 46 CFR 541.8, Requests for fee mitigation, refund, or waiver (Cornell LII)
- 46 CFR Part 541, Demurrage and detention billing requirements (Cornell LII)
- 49 CFR 378.2, Definitions of overcharge, duplicate payment and overcollection (Cornell LII)
- 49 CFR 378.8, Overcharge claim resolution within 60 days (Cornell LII)
- 49 U.S.C. 13710, Billing and contesting windows (Cornell LII)