Demurrage & Per Diem Calculator
Put in the Last Free Day and the day you actually expect to move the box. This works out both clocks — demurrage inside the terminal and per-diem once it is on the street — using the tiered daily rates carriers actually bill.
Default demurrage tiers are the shape most ocean carriers use at Seattle and Tacoma: the daily rate steps up the longer the box sits. Your tariff will differ — treat this as the order of magnitude, not the invoice.
The two clocks, and why they overlap
Importers lose money here because they think of it as one charge. It is two, billed by the same carrier, for opposite sides of the same gate:
- Demurrage — the box is still inside the terminal past its free time. Expensive, tiered, and the terminal is not obliged to give you an appointment to stop it.
- Per-diem (detention) — you have the carrier's container outside the terminal and have not given it back. Cheaper per day, but it runs quietly for weeks.
The dangerous week is the one where they overlap: you pull a box late, so demurrage already ran, and then the empty return appointment is full, so per-diem runs too. One container, two meters.
Where the days actually go
Almost every demurrage bill we see traces back to one of four things, and none of them is the driver being slow:
- The LFD was never tracked from discharge, so nobody knew the clock had started.
- The appointment grid was full when someone finally looked — terminal slots go days out in peak.
- A hold was on the box (customs, freight, line) and nobody cleared it while the free days burned.
- The warehouse had no door for it, so the box sat gated-in waiting on a receiving slot.
The structural fix is boring: one party watching the LFD, the appointment and the dock door at the same time. When drayage and the warehouse are separate vendors, the free days are burned in the gap between them — see how we run drayage and our full guide to LFD, demurrage and per-diem.
Questions we get asked
What is demurrage?
Demurrage is what the ocean carrier charges when your loaded container sits inside the terminal past its free time. The clock starts the day after the Last Free Day and runs until the box leaves the gate. It is billed per container per day and the daily rate climbs in tiers the longer the box sits.
What is the difference between demurrage and detention?
Demurrage is charged while the container is still inside the terminal. Detention - often called per-diem - is charged once you have pulled it out and are holding the carrier's equipment on the street or in your yard. Same idea, opposite side of the gate, and on a bad week you can be paying both on the same box.
When does the demurrage clock start?
The day after the Last Free Day, not on it. The LFD is the last day you can still pull the box for free, so a container gated out on its LFD owes nothing. Free days are usually counted in calendar days, which is why a Thursday LFD over a holiday weekend is far more dangerous than it looks.
How do you avoid demurrage charges?
Track the Last Free Day on every container from the moment it is discharged, book the terminal appointment as soon as the box goes available, and pre-pull to your own yard when the appointment grid is tight. Pre-pull moves you off the expensive terminal clock and onto the cheaper per-diem one.
Want the clock watched for you?
We track the Last Free Day on every container from discharge, book the appointment early, and pre-pull to our Kent yard when the grid is tight.
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