What is the difference between demurrage, detention and per diem?

Two clocks, in two places

Demurrage runs inside the terminal. A loaded import container gets a number of free days once it is discharged and available for pickup. After its last free day, the ocean carrier or the marine terminal bills for every day it stays. The clock stops when the container leaves the gate.

Detention runs outside. Once the container leaves the terminal, the carrier allows a number of free days to unload it and bring the empty back. After that it bills detention, which US carriers usually call per diem, “per day”, until the empty is returned. A slow unload, a warehouse short of dock doors or a terminal that won’t take empties back can all keep that clock running.

Free time for each is set in the carrier’s tariff, the terminal’s schedule or your service contract, and some contracts combine the two into one allowance. Ask which applies to you, and whether weekends count.

Who bills which

Demurrage comes from the ocean carrier or the marine terminal operator, depending on the port and the terminal. Per diem comes from the ocean carrier, because it owns or leases the container. Either can reach you directly or as a pass-through line on your forwarder’s invoice. Truckers have their own “detention” for time a driver waits at a dock; Freight Benchmarks reports that separately as driver waiting time.

How often each hits, and what it costs

Most shipments pay neither. In Freight Benchmarks’ invoice data, 2.4% of shipments paid demurrage and 3.7% paid per diem. The ones that pay can pay a lot: 1 in 10 demurrage bills was over $2,870 per shipment, and 1 in 10 per diem bills was over $2,370. Both are counted per shipment; most shipments are a single container.

The same billing rule covers both

The Federal Maritime Commission’s billing rule for demurrage and detention, 46 CFR part 541, defines “demurrage or detention” to include per diem. An ocean carrier or marine terminal operator has to issue the invoice within 30 days of the last day the charge accrued (an NVOCC passing one on has 30 days from that invoice), and every invoice has to carry the details the rule lists. One that misses either doesn’t have to be paid. The steps are in how to dispute a demurrage or detention invoice. This is general information, not legal advice.