Demurrage and detention software: whose calendar?

Every product sold as demurrage and detention software stores a number of free days somewhere. The question worth asking in a demo is not how many days it holds. It is what it thinks a day is.

Five published tariffs this site has now read, across four countries, disagree on that, and they disagree in three independent ways at once.

The two that are exact opposites

Ocean Network Express’s Singapore agency tariff allows four working days of inbound demurrage. Its own note defines the unit:

Work days, where mentioned refers and excludes Saturday, Sunday and Public Holidays declared by the Ministry of Manpower, Singapore.

Adani’s Mundra terminal tariff allows two free days on a road-evacuated import container, counted “from the day of landing, up to the day of loading, delivery or removal of the container, and including Sundays and holidays”, where “per day” means “per calendar day or part thereof”.

One excludes weekends and a national holiday calendar. The other explicitly includes them. Both are the current published document for their port. A field called “free days” holds the same integer for both and is wrong about one of them.

What that costs, arithmetically

Take a box discharged at Singapore on Friday 13 February 2026. Chinese New Year falls on the Tuesday and Wednesday of the following week. The four working days land on Monday the 16th, Thursday the 19th, Friday the 20th and Monday the 23rd. The allowance expires on Monday 23 February — ten calendar days after discharge.

The same four working days on a box discharged on a Monday in an ordinary week expire on the Friday: four calendar days. One tariff, one port, one allowance, and the deadline moves by six days depending on which day the vessel worked.

A reminder set for “day 4” is wrong in both cases: early in February, and on time only by accident in April. Six days of error at about US$12,000 for a week of demurrage on one container is not a rounding problem.

Day zero is a third variable, and nobody agrees on it

The counting unit is only half of it. The tariffs also disagree about which day the count starts on:

Nhava Sheva starts a day later than Mundra on the same event. On a three-day allowance that one day is a third of the free period. And NSICT adds an exclusion of its own: free dwell time there is “exclusive of customs notified holidays and port non-working days”, which is a different calendar again from the Ministry of Manpower’s.

So there are three settings, not one: day zero, whether non-working days count, and whose list of non-working days. No two of these five tariffs answer all three the same way.

The question that finds out

Most demurrage and detention tools are built on a container-tracking feed. A feed gives you events: discharged, gated out, empty returned. Turning an event into a deadline is the part that needs the tariff, and the tariff is the part nobody ships with the product.

So in the demo, ask to see the screen where you set the rule. Not the screen that shows the countdown, but the screen where day zero, the weekend rule and the holiday calendar are configured, per terminal and per carrier. If that screen does not exist, the countdown on the dashboard is a subtraction, and you will find out which lane it was wrong about when the invoice arrives.

While that screen is open, check the field above the day count as well: the carrier the figure was read from. On a booking moving under a house bill of lading the carrier on your bill of lading may not own a ship, and a tool resolving free time from the vessel operator is quoting a contract you are not party to: counted perfectly, out of the wrong tariff.

Then ask the second question, which is the one that decides the money: when the allowance is about to be spent because a supplier has not sent the certificate, what does the product do? Document packs routinely run about eight days late. Against four working days at Singapore or two at Mundra, the allowance is gone before the pack is complete, and nothing about counting it more precisely fixes that.

Counting correctly is the minimum. Demurrage and detention software that counts in the tariff’s own unit and then goes and chases the missing paper is the part that changes the invoice. If you want to work out what an overstay cost on your own lane, the demurrage calculator takes the free days and the per-diem tiers off your own contract. Now you know to check what kind of day you are typing in.