Port congestion: reading demurrage and per diem before they bite

A container clears customs and sits. The terminal is backed up, chassis are scarce, or the receiving warehouse can't take the load yet. Nobody moved anything wrong — but the clock on demurrage and per diem is already running, and by the time someone notices, the charges have piled up past what anyone budgeted for.

This is the moment most shippers and carriers actually meet these terms for the first time: not in a contract review, but in an invoice they didn't expect.

Two different clocks, two different owners

Demurrage and per diem sound like the same thing and get used interchangeably, but they charge for different problems.

• Demurrage is what the ocean carrier or terminal charges for a container that stays in the port or terminal past its free time, whether it's loaded or empty.
• Per diem (sometimes called detention) is what the ocean carrier charges for use of its equipment — the container and chassis — once it leaves the terminal and isn't returned on schedule.

In practice, a box can rack up demurrage while it's still sitting in the yard, then start racking up per diem the moment it's picked up and the return clock starts, even if it never gets close to being late for delivery. The two clocks can run one after another, and in a bad week, they can overlap.

Why the free time runs out faster than expected

Every shipping line and terminal sets its own free time, and it varies by port, by contract, and sometimes by season. Congestion doesn't lengthen that window — it just makes it harder to use. A chassis shortage, a truck slot that doesn't open until next week, or a warehouse that's still working through last month's backlog all eat into free time that was already tight before the ship docked.

The charges exist to keep containers and equipment moving through a terminal that has limited space. That's a reasonable goal from the terminal's side. It's a real cost from the shipper's or carrier's side when the delay isn't caused by either of them.

What actually helps

There's no way to make a congested port move faster, but there are ways to reduce how much of the delay lands on your invoice:

• Know the free time terms for the specific port and carrier before the vessel arrives, not after the container is already sitting.
• Line up drayage and chassis availability ahead of the container's arrival, not once it's already on the ground.
• Confirm the receiving dock can actually take the load on the day you're planning to deliver it — a truck that arrives and waits is still burning per diem.
• Ask who is contractually responsible for demurrage and per diem before the load moves, not after the charges show up.

That last point matters more than it sounds. Terms vary by carrier, by mode, and by who booked the container, and it's rarely obvious from the bill of lading alone which party is on the hook.

Where a broker's carrier vetting fits in

Part of avoiding these charges is having drayage and trucking capacity that's actually available when the container is ready, not capacity that has to be scrambled together after the fact. Ellys International Logistics works with an invite-only carrier network that's checked against live FMCSA data before dispatch, which is one piece of keeping the pickup side of this timeline predictable instead of reactive.

If you're moving freight through a congested port or across the US-Mexico border and want to see what capacity looks like on your specific lane, visit /lanes.