Three charges show up on import invoices, they all mean roughly “your container sat too long,” and importers mix them up constantly. They are billed by different parties, the clocks run at different times, and the way you avoid each one is different. Getting them straight is worth real money.
Demurrage: The Container Is Still Inside the Terminal
Demurrage is charged by the ocean carrier for a loaded container sitting at the terminal past its free time. The clock starts when the container is available for pickup — discharged and released — and stops when it leaves the gate.
The important nuance is that availability is not arrival. A vessel can discharge on Monday and the box might not be released until Wednesday. Your free time runs from release, not from when the ship tied up.
Detention: The Container Is Out, and Still Yours
Detention is also charged by the carrier, but it covers the period after the container has left the terminal and before you return it empty. It is the carrier saying: that is our equipment, you are still holding it.
This is the one that catches people who unload slowly. You beat demurrage by pulling the container out on day three, then let it sit at your dock for a week because nobody scheduled labour to strip it. The demurrage clock stopped and the detention clock started.
Per Diem: Usually the Same Thing, Sometimes Not
Per diem is often used interchangeably with detention, and in most conversations they mean the same charge. Where it can differ is chassis. If the chassis came from a pool rather than the carrier, you may see a separate daily charge for it, billed by the pool operator, running on its own clock.
The practical point: read the invoice line by line rather than assuming one daily charge. It is possible to be paying two clocks at once on the same container.
How Much Free Time You Actually Have
There is no universal answer, and this is where most bad assumptions start. Free time is set by your contract with the carrier, not by the port, and it varies by carrier, by trade lane, and by how much volume you move. Some shippers negotiate significantly more than the default. Some forwarders quote you a rate that quietly assumes the minimum.
Two things are worth checking on every shipment: how many days you have, and whether they are calendar days or working days. Over a holiday weekend that distinction is the difference between clean and expensive.
Where the Money Is Usually Lost
In our experience the expensive containers are rarely the ones with a genuine problem. They are the ones where nobody owned the timeline. The broker assumed the warehouse knew the arrival date. The warehouse assumed the freight was cleared. Nobody looked at the container until day five.
Three habits fix most of it. Clear customs before the vessel berths. Book the unload slot at the same time you book the truck, not after. And if you cannot take delivery inside free time, transload the freight instead of holding the box — strip it near the port, return the empty, and move the product on a regular trailer that costs nothing per day to keep.
That last option is the one importers forget exists, and it is often the cheapest answer to a container you are not ready for.
We run transload and crossdock operations from an 80,000 square foot facility in Doral, minutes from PortMiami. If you have a container arriving and no room for it, get in touch before the free time runs out rather than after.