Two clocks, not one
Import demurrage free time covers how long the packed container may sit inside the terminal after the line's start event — commonly the day of discharge, sometimes the day the box is available for pickup. Once that allowance is used, demurrage accrues while the box occupies terminal ground. Detention free time is a second allowance that usually starts when the container gates out, covering how long the consignee may keep the carrier's equipment for unpacking and empty return.
Export free time runs the other way: how long you may hold the empty for stuffing and how long the packed box may sit at origin before load. Desks that only watch the import demurrage clock still get surprised by origin export detention on a late-stuffed booking.
When the clock starts — the argument that costs money
Tariffs disagree on the start event. 'Discharge date' starts the day the crane lands the box, even if customs, holds, or a missing telex make it uncollectable. 'Availability date' starts when the terminal says the box can actually be gated out. A weekend discharge with Monday availability can be two free days or zero, depending on that sentence. Always read the carrier's rule for that port, not the last invoice you paid.
Worked sequence: vessel completes discharge Friday 16:00. Tariff is four calendar days from discharge, including the day of discharge. Saturday and Sunday count. Free time ends Monday. If the importer's broker cannot file until Tuesday morning, Tuesday is already on demurrage — even though nobody could have collected the box on the weekend. A working-day tariff would have skipped Saturday and Sunday; a calendar tariff does not.
Calendar days, working days, and combined D&D
Calendar days count every day including weekends and public holidays. Working days skip weekends and, sometimes, port holidays — 'sometimes' is the trap; some lines skip Sundays only. Combined D&D (also called merged or total free time) gives one pool of days that covers both in-terminal and out-of-terminal use. Split D&D gives two separate pools. Combined looks generous until a slow unpacking eats the days you needed at the terminal.
The demurrage versus detention page covers what each charge is. This page is the clock: without knowing start event, day-type, and split versus combined, you cannot forecast exposure. Service contracts often buy extra free time on specific ports; spot FAK boxes sit on the published tariff. Quoting a door-move without reading free time is how a cheap ocean rate becomes an expensive file.
What free time is not
It is not terminal storage. Some ports bill storage to the merchant in parallel with carrier demurrage. It is not a customs hold waiver — a hold can run the clock while the box is uncollectable, which is why pre-arrival filing and telex or seaway release matter. It is not guaranteed by the booking confirmation unless the confirmation cites a contract clause. If the SI is late and originals are still in a courier pouch, free time does not pause for documents.