Demurrage is the charge an ocean carrier bills when a full import container sits inside the terminal beyond its free time; detention is the charge when you hold the carrier’s container or equipment outside the terminal beyond free time. Free time is the number of calendar days before each clock starts.
In short: demurrage = the box is still at the port; detention = you have the box but haven’t returned the empty. Free days, and the daily rate after them, vary by carrier, port, and contract.
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DCSA Track & Trace · Container number (ISO 6346) · Bill of lading (B/L) · Transshipment · UN/LOCODE