Port congestion: reading demurrage and per diem before they bite

A container lands at the terminal and the free time clock starts immediately, whether or not the drayage carrier has an appointment, whether or not customs has released the entry, and whether or not anyone back at the office is actually watching the date. By the time someone checks the terminal portal, charges may already be accruing. This is how most demurrage and per diem disputes begin: not with a bad actor, but with a gap in who was watching the clock.

Demurrage and per diem are not the same charge

Demurrage is charged by the terminal or port for a container that stays on their property past its free time. Per diem (sometimes called detention, depending on the ocean carrier and the mode) is charged by the ocean carrier or equipment owner for the container or chassis itself, once it leaves the terminal but isn't returned empty on schedule. A shipper can clear demurrage and still rack up per diem if the empty sits at a warehouse too long before going back.

Both charges exist for the same basic reason: equipment and yard space are finite, and the owner wants it back in circulation. The charges are not usually negotiable after the fact. They are built into the tariff or the service contract and they start on a date, not on a judgment call.

Free time is set before the cargo even ships

Free time windows vary by port, by ocean carrier, and sometimes by contract negotiated in advance. There is no single standard number of days, and claims that there is one should be treated with suspicion. What matters is that the free time terms are usually set long before the vessel arrives, which means they can and should be checked in advance rather than discovered after the invoice shows up.

Where congestion makes this worse

Port congestion does not usually extend free time. It just makes it harder to get the container moved before free time runs out. A chassis shortage, a terminal with limited appointment slots, or a customs hold can all eat into the window without changing the billing clock. The result is a charge that looks like a penalty for the shipper's inaction, even when the delay sat somewhere else in the chain entirely.

Practical steps that actually reduce exposure

• Track the vessel and container status daily once it's within a week of arrival, not just at discharge.
• Confirm the customs entry is filed and cleared before the container hits the terminal, not after.
• Line up the drayage appointment and chassis availability ahead of the ship's arrival rather than after.
• Know who is contractually responsible for demurrage and per diem on this specific shipment, since it varies by agreement between shipper, consignee, and carrier.
• Return empties promptly and keep the paperwork showing the return date, in case per diem is disputed later.

None of this eliminates congestion. It does shrink the number of days where nobody is actively managing the container, which is where most avoidable charges come from.

Why this matters more on cross-border moves

On US-Mexico freight, the same clock runs alongside a cross-border handoff, and a missed appointment or a customs delay on one side can cascade into port or yard charges on the other. Ellys International Logistics works the US-Mexico corridor specifically, with bilingual coordination between shippers, carriers, and brokers so that a delay gets flagged in both languages at the same time it happens, not after the invoice arrives.

Ellys vets every carrier in its network against live FMCSA data before dispatch and keeps monitoring them through the move, which is part of how a load gets tracked closely enough to catch a free-time window before it closes.

If you're trying to get ahead of a congested lane before it costs you, visit /lanes to see the corridors Ellys covers and start the conversation.