What a demurrage spreadsheet cannot hold

Ask an import desk where its free time lives and you will usually be shown a spreadsheet. A row per shipment, a column headed free days, a formula that adds it to the discharge date, and conditional formatting that turns the cell amber near the end. It is a reasonable piece of work. Somebody built it because nothing else on the desk held the date at all.

The problem is not that the arithmetic is fragile. It is that the tariff the arithmetic is standing in for is not a number. It is a function, and the published documents say so in detail.

Here is what a single cell has to swallow, taken from five current terminal tariffs at Nhava Sheva and one at Jebel Ali.

One: which terminal worked the vessel

Nhava Sheva has five container terminals and each files its own Scale of Rates with the port authority. An import loaded container gets three free days at NSICT and NSFT and two at NSIGT, GTI and BMCT. Jebel Ali gives an ordinary import box ten.

The importer does not choose. Berthing does. So the free-days figure is not a property of the lane, the carrier or the port, and cannot be filled in when the booking is made, which is exactly when a spreadsheet row gets created. The per-terminal detail is on the Nhava Sheva port page.

Two: which band the day falls in

A spreadsheet stores a rate per day. Tariffs are written in escalating slabs.

At NSICT an import container costs US$9.33 a day for a 20ft box in days 4 to 15, then US$18.64 in days 16 to 30, then US$37.28 beyond 30, doubling and doubling again. BMCT steps through nine bands, from ₹799.59 a day at days 3 to 6 up to ₹3,196.14 thereafter. NSFT uses seven.

The consequence is not academic. A four-day overstay doubled is not an eight-day overstay, and a desk that models the cost of delay as days × rate will forecast the cheap end of a curve that bends upward precisely when things are going badly.

Three: the size band, and there are three of them

Most desks carry 20ft and 40ft. Every tariff quoted here carries a third column for containers above 40ft, charged higher again: US$27.99 a day against US$18.66 at NSICT in the first paid band. A 45ft box priced off the 40ft column is under-accrued on every day it sits.

Four: what is inside the box

Hazardous cargo is charged more at all five Nhava Sheva terminals and by a different factor at nearly each one: 25% more at NSICT, 1.25 times at NSIGT and BMCT, 1.5 times at GTI, and 2 times at NSFT. Over-high and over-dimensional containers attract three times the normal charge across all five.

At Jebel Ali the same idea is expressed even harder: IMDG class 5 gets no free time at all. Cargo class is not a note on the shipment. It is a term in the formula.

Five: the currency, fixed on a date that has passed

Three of the five Nhava Sheva terminals denominate storage in dollars and collect rupees. NSFT’s tariff spells out the mechanism: the dollar charge is reconverted at a public sector bank’s market buying rate “prevalent on the date of entry of the vessel into the port limits” for import containers. NSICT applies the same rule.

So the conversion rate is fixed on a date in the past, and it is not the invoice date. A spreadsheet that holds a rupee figure holds an estimate of an amount that was decided when the ship arrived.

Six: the edition

NSICT’s and NSIGT’s current Scales of Rates both carry an indexation of 0.39%, effective 1 May and 1 April 2026, granted under the same letter. GTI’s document states the standing rule rather than this year’s result: the tariff “is subject to automatic annual indexation at 60% of the WPI”, from 1 May every year.

Rates typed into a system therefore have a decay date, and nothing in the spreadsheet knows it. This is the variable that goes wrong quietly, because the formula keeps working.

What this argues, and what it does not

It does not argue that the desk needs a better calculator. Run the numbers above through anything you like: a container that clears inside its free days costs none of it.

The reason a box goes past its last free day is almost never that the arithmetic was wrong. It is that a certificate of origin had not arrived, an invoice disagreed with the packing list, or the customs broker was waiting on a delivery order nobody had settled, and the days ran out while three people each believed somebody else was chasing. Document packs routinely run about eight days late. Against two free days at BMCT, the allowance is spent before the pack is complete.

So the honest test to put to any demurrage and detention software you are being sold is two questions, in this order. Does it hold all six variables above per shipment, rather than one free-days field per carrier? And when the pack is not ready on day three, does it chase the party who owes the document, or does it show you a coloured chip?

The first question decides whether the tool is more accurate than your spreadsheet. Only the second decides whether it prevents anything. If you are replacing a spreadsheet across the whole desk rather than only the clock, we wrote about what actually breaks when import tracking lives in Excel separately; and if the number you want today is what an overstay would cost, the demurrage calculator takes the free days and the per-diem tiers off your own contract.