Demurrage and detention are often confused but describe different charges in different contexts. Demurrage is the ocean shipping and rail term for containers held at the carrier's terminal beyond free time. Detention, in the ocean context, is for containers held at the importer's facility beyond free time — the mirror image of demurrage.
In over-the-road trucking, "detention" covers all waiting time charges at pickup or delivery, and "demurrage" is typically not used. Understanding the context matters because mixing the terms creates invoice disputes.
Demurrage free time is the period after a container is discharged from a vessel (or unloaded from a train) and made available for pickup during which no charges accrue. Shipping lines typically offer two to five free days depending on the port, the trade lane, and any negotiated contract terms. After free time expires, demurrage accrues at a daily rate that escalates in tiers — the longer a container sits, the higher the daily rate.
The primary driver of demurrage is a mismatch between the importer's supply chain and port operations. Port congestion, warehouse unavailability, customs holds, trucking appointment shortages, and chassis scarcity all contribute. During supply chain disruptions, demurrage has been a source of significant unexpected cost for importers who lacked real-time visibility into port conditions and container availability.
Managing demurrage requires active monitoring of container availability notices, proactive scheduling of drayage appointments, and warehouse capacity that can receive containers promptly after port release.