The container cleared customs days ago and nobody moved it. By the time the truck shows up, the line has run three rate tiers and the invoice is four figures per box. Demurrage and detention are the charges that quietly wreck a shipment’s margin, and they climb faster than most people expect because the per-diem escalates.
Enter the free time and the rates and see where it lands.
CargoEZ tracks free time, last free days and container status across shipments so demurrage and detention get flagged before they pile up. Built for freight forwarders.
Demurrage versus detention
The two get mixed up constantly, and they are charged by the same logic but for opposite situations. Demurrage is what the shipping line charges while your loaded container sits inside the terminal past the free time, waiting to be picked up. Detention is what it charges once you have taken the container out and are holding it at your warehouse or yard past the free time, before you return the empty.
Chargeable days = Days held − Free days
Charge = chargeable days priced across the rate tiers × number of containers
Same container, two clocks. One runs at the port, the other runs at your dock, and a slow unload can trigger both on a single box.
Escalation is what hurts
Lines do not charge a flat daily rate. They tier it, and each tier is higher than the last, because the point is to get the box back, not to earn rent. A common pattern is a moderate rate for the first few chargeable days, a higher one for the next band, and a steep one beyond that.
The math is unforgiving. Twenty chargeable days at $150, then $250, then $400 is $6,000 per container, double what a flat $150 would suggest. On a ten-container entry that is $60,000, and it accrues whether or not anyone is watching the free-time clock. The calculator tiers the rates the way the carrier does, so the number you see is the number on the invoice, not an underestimate.
Worked example
One container, picked up 6 chargeable days late, returned 4 chargeable days late, at typical US rates.
| Charge | Chargeable days | Rate build-up | Cost |
|---|---|---|---|
| Demurrage | 6 | 5 × $150 + 1 × $250 | $1,000 |
| Detention | 4 | 4 × $100 | $400 |
| Total | $1,400 |
Multiply across the containers on the entry and the free-time window becomes the single most important date in the shipment. For the container capacity and load planning that keep boxes moving, use the container load calculator. More tools are in the freight forwarding calculators section.