What is Detention?
Detention is the charge for keeping a carrier's container outside the terminal or depot beyond the allowed free time: on imports from gate-out of the full container until the empty is returned, and on exports from pickup of the empty until the loaded container is delivered back to the terminal. In US trades it is often called per diem, and the FMC treats demurrage and detention together in 46 CFR 541.3 as charges for the use of terminal space or shipping containers, excluding freight. Free days and daily rates are set in carrier tariffs or service contracts, commonly in escalating tiers and varying by equipment type. Truckers face a parallel regime for equipment use under the Uniform Intermodal Interchange and Facilities Access Agreement (UIIA) in North America, administered by the Intermodal Association of North America. The FMC's interpretive rule states that detention charged when empty containers cannot be returned is likely to be found unreasonable (46 CFR 545.5).
Why it matters for forwarders
Detention is driven by inland operations: slow unloading at the consignee, warehouse appointment delays, trucking capacity and depot restrictions on empty returns. Give consignees the exact free time and last return date before the container leaves the terminal, and record every day a depot refused empties or appointments were unavailable, because that evidence supports disputes. In US trades, detention invoices follow the same FMC rule as demurrage: issued within 30 calendar days of when charges were last incurred, with the required content, and open to dispute for at least 30 days. Where the carrier arranged inland delivery (carrier haulage), check whether the delay was caused by the carrier's own trucking before accepting charges. Combined demurrage and detention free time in service contracts gives flexibility when delays shift between port and inland.