Free tool
Demurrage and detention are two different clocks.
One runs while the box is still inside the port. The other runs while it is out in your yard. They have separate free days, usually separate rates, and a container can be running up both in the same week for different reasons — a customs hold on one clock, a slow unload on the other. Put your own dates in and this works each container separately, then shows which clock the money came off.
Nothing you type leaves your browser. There is no account, no form and no file upload — the calculation runs in the page.
Your shipping terms
From your own contract.
Leave a date blank on a container to say it has not happened yet. An empty collection date means the box is still in the port; an empty return date means it is still out. Both are counted up to the date above, which defaults to today.
The containers
Three dates each.
The distinction
Why one pool of free days gives the wrong answer.
| Clock | Runs from | Runs to | What it is really measuring |
|---|---|---|---|
| Demurrage | The day the box was available | The day you collected it | The port's storage. Customs holds, missing documents, a truck you could not get. |
| Detention | The day you collected it | The day the empty went back | The carrier's box, out of circulation. Your yard, your unloading, your return leg. |
Detention does not start until the box is collected. A container still sitting in the port is running up demurrage and is not yet out on detention, and counting it on both is the most common reason a self-made estimate comes out higher than the carrier's invoice. The table above marks an uncollected box as not collected rather than giving it a detention figure.
The two clocks also point at different people. Demurrage is usually a documentation or clearing problem; detention is usually a yard or transport problem. A single blended number tells you that you paid — it does not tell you who to talk to on Monday.
Said before you ask
This uses one flat rate per day.
Real carrier tariffs are usually slabbed — a few free days, then a rate, then a higher rate past day ten or fifteen — and the slabs differ by carrier, by port, by box type and by what your contract says. There is no slab table here and there is none in SIAARU either: the product takes a day rate from each organisation's own shipping terms and multiplies. A calculator that produced a slabbed figure from a tariff it had invented would be claiming a capability the product does not have, on a site whose published commitment is never to invent a number.
So put your real rates in. If your contract is slabbed and you want the exact figure, this will get you the chargeable days right — which is the half that is actually hard — and the rate is then a lookup you can do against your own tariff.
Two more things it does not do, which the product does: it reads the containers you type rather than every container on every shipment, and it forgets everything the moment you close the tab. Watching this across a live shipment book, telling you which boxes are accruing today while there is still time to move them, and ranking the freight bill by what is avoidable is what EXIMGuard and FreightAudit AI do, on the same engine as the rest of the platform.