Ask three different people in a supply chain what “detention” means and you can get three different answers. The steamship line means one thing, the trucker means another, and the importer paying the invoice often isn’t sure which charge just hit their account. That confusion isn’t harmless. It’s exactly why these fees get paid when they shouldn’t, and disputed too late when they should.
There are three separate charges that show up on drayage moves. They bill for different things, start on different clocks, and get paid by different parties. Here’s the clean version.
The one-line version
Demurrage is the loaded container sitting inside the terminal past its free time. Per diem is the steamship line’s container staying out past its free time, and the clock starts the moment it leaves the gate. Detention is the driver and truck stuck waiting. Same move, three meters, and only one of them has anything to do with where the box physically sits.
| Charge | What it bills for | Who bills it | When the clock starts | When it stops |
|---|---|---|---|---|
| Demurrage | Loaded container occupying space inside the terminal past free time | Terminal / ocean carrier | When free time expires after vessel discharge | At gate-out (pickup) |
| Per diem | The carrier’s container held out of the terminal past free time | Steamship line (SSL) | At gate-out, the moment the box leaves the terminal | When the empty is returned to the depot |
| Detention | The driver and truck held past the free window | Drayage carrier | When the free window (usually 1–2 hrs) expires at a stop | When the driver is released |
Demurrage: the box hasn’t left yet
Demurrage runs while the loaded container is still inside the terminal. The vessel discharges, free time starts, and you have a window, commonly four to seven days at U.S. marine ports, to get the box picked up. Miss it and the terminal starts charging per container, per day, on a tiered scale that climbs the longer it sits.
Two things trip people up here. The first is that “demurrage” often isn’t a single clearance. There’s the steamship line’s side and the terminal’s side, and how you clear them depends entirely on the facility. At some terminals you clear both in one step. At others you have to clear the line’s hold first and then settle the terminal’s demurrage separately. At still others the steamship line can release both. If you assume one payment closes it out everywhere, you will eventually find a box that’s “paid” and still won’t release.
The second is that the last free day itself isn’t always one number. The steamship line’s LFD and the terminal’s LFD on the same container don’t always match. Watching only one of them is how a box you thought had a day left starts accruing. Watch both.
Rail is its own case. Once a container is grounded at the ramp, free time is typically much tighter than at a marine terminal, often around two days. On intermodal moves that short window is the thing that bites, because the clock is running almost as soon as the box hits the ground.
The core point stays simple: demurrage is a space charge. The terminal wants the box gone so the slot is free for the next one. Avoiding it comes down to being ready to pull the container the day it’s available, with the appointment booked, the chassis lined up, and the trucker dispatched.
Per diem: the clock starts at the gate
This is the one that gets described wrong most often, so we’ll be precise: per diem is a clock, not a location. The moment the container out-gates the terminal, the steamship line’s free-time clock on their equipment starts running. It does not matter where the box goes next: on a chassis, at your dock, in a drop yard, parked on the street. What matters is that it left the terminal and hasn’t come back. The clock stops only when the empty is returned to the designated depot.
So per diem bills you for holding the carrier’s container out in the world past the free days they gave you. Gate-out starts it; empty return ends it. A box pulled clean off the terminal on day one but sat at a warehouse for a week waiting for a return appointment is racking up per diem the entire time, even though it never touched a demurrage charge.
That gate-out line is the whole distinction between demurrage and per diem. Before the gate: demurrage. After the gate: per diem. They can’t both run at once on the same container, and they hand off at exactly that moment.
Detention: the driver is the one waiting
Detention is a different animal entirely, and mixing it in with the other two is where a lot of the confusion starts. Detention isn’t about the container’s clock at all. It’s about the driver and truck being held. A trucker arrives at the terminal, the rail ramp, or the consignee’s dock, and gets a free window to load, unload, or turn, usually one to two hours. Past that, the drayage carrier bills detention, by the hour, for the time the driver and equipment are stuck doing nothing.
You can rack up detention on a move that never sees a dollar of demurrage or per diem. A driver sitting four hours in a terminal queue is detention, full stop, regardless of how the container’s own clocks are running. It’s the cost of a person and a truck being unable to do anything else.
What blows through free time
None of these charges exist because someone was careless. They pile up because a container’s journey has a dozen handoffs and any one of them can stall:
- Terminal congestion: no appointment slots, or a line so long the free days burn before you can physically get in.
- Missing chassis: the box is ready but there’s no chassis to put it on, a chronic problem at the busiest gateways.
- Customs or PGA holds: the container can’t move until it’s released, and the clock doesn’t care why.
- Empty return restrictions: the depot won’t take the empty back, or changes where it can go, stranding the box out on per diem.
- Warehouse or receiving bottlenecks: no dock slot to unload into, so the box waits.
The through-line: these clocks run in parallel and feed each other. A chassis shortage that delays pickup can push you into demurrage; the same shortage that delays the empty return pushes you into per diem. The way you keep them all down is to treat pickup, unload, and empty return as one scheduled chain, not three separate hopes, and to watch the last free day on every container like it’s a deadline, because it is.
Who eats the cost
This is where it gets contested, and the honest answer is that it depends on whose fault the delay was.
If the delay is on your side, you were slow to dispatch, your warehouse couldn’t take the box, you booked the return late, the charge is generally yours. That’s the carrier or terminal charging you for tying up their asset because of something in your control.
A share of these fees stem from things the shipper couldn’t control, and those are worth disputing. If the terminal was closed, refused the empty, or the delay was clearly on the facility’s side during your free days, that’s the kind of situation where invoices get reversed. A steamship line or terminal will sometimes waive a charge when the delay was demonstrably their fault, their congestion, their gate closure.
But temper the expectation, because waivers are not automatic and some grounds are weaker than they look. “No chassis available” is the classic example. It feels like the terminal’s problem, but private and pool chassis are usually an option, so whether a chassis shortage clears anything is entirely terminal-dependent. Plenty of terminals won’t waive on that basis at all, precisely because an alternative existed. Go in assuming every waiver has to be argued, not granted.
The lever that makes waivers actually happen is documentation. Keep everything: gate tickets, appointment confirmations, terminal screenshots showing no slots, empty-return receipts, timestamps. A dispute backed by a screenshot of a closed return window has a real chance. A dispute backed by “we’re pretty sure it wasn’t our fault” does not.
The rules changed, twice
Two recent developments make this worth revisiting even if you thought you had it handled.
First, the Federal Maritime Commission’s Demurrage and Detention Billing Rule took effect in May 2024. It tightened what carriers can bill and how: invoices have to arrive within a set window, charges have to be itemized per day, and the correct paying party has to be named. An invoice missing required fields is disputable on that basis alone. The rule gave shippers a real, procedural path to push back on sloppy billing, separate from the fault question.
Second, and more recently, a 2025 federal court ruling unwound part of who the FMC could dictate gets billed. The practical fallout: protections that used to be guaranteed by regulation now have to be secured in your contracts. Billing-party language, per diem rate caps, free-time terms: if your agreements with ocean carriers, NVOCCs, or drayage providers don’t spell these out, you’re exposed to whatever the published tariff says, which is almost always worse than a negotiated rate. Anyone renewing a freight agreement right now should be treating these as required terms, not fine print.
The practical takeaway
Most of what drives these charges is timing, and most of the timing is manageable with visibility and a partner who watches the clocks for you. On our own port-to-Vegas moves out of Long Beach and Los Angeles, the containers that stay clean are the ones where pickup, unload, and empty return were scheduled as a single chain and the last free day was flagged before it arrived, not discovered on an invoice two weeks later.
Know which charge is which. Watch the free time on every box. Document everything the moment something stalls. And read your carrier contracts like the tariff is the fallback, because now, more than before, it is.