Customs Demurrage Penalty Tracker
First billable penalty day when a container overstays port free time.
Written and maintained by Paul Clark, Redmoon Software · Rules last verified · Sources · Changes & corrections
These calculators are for informational purposes only and do not constitute legal, financial, or professional advice.
How the Customs Demurrage Penalty Tracker works
The Customs Demurrage Penalty Tracker takes the date a container becomes available at the terminal and the number of free days your carrier grants, and returns your last free day — the final day before demurrage starts billing. Enter the availability date, the free-day allowance, and whether those days are counted as calendar or working days; the tool counts forward, skipping the holidays of the port country you select, and reports the result as the deadline by which the box has to be off the terminal. The first billable day is the day after the date it shows.
The clock anchors to availability — typically discharge from the vessel and customs release, summarized by the terminal as a posted Last Free Day — not to the day your trucker or warehouse is ready. That start date governs everything, so confirm it from the terminal before you count. Free time is a carrier grace period, commonly a few days, defined by the carrier's tariff and your service contract rather than by law.
Whether free days run in straight calendar days or only working days changes the answer, sometimes by several days when a long weekend or port holiday falls inside the window. The "Use business days" toggle is ticked by default, which matches the common US pattern: tariffs such as the Port of Los Angeles’s count free time exclusive of Saturdays, Sundays and holidays, and carriers such as Maersk count it on days the pickup gate is open. Untick it for a tariff written in calendar days, and free time then runs straight through weekends and holidays; a last free day on a Saturday stays on the Saturday, and the result warns you to check the gate hours. Only if your tariff says free time ending on a non-working day is extended should you tick the extension box. Set the count to match your tariff, read the result as your last free day, and treat the following day as the first on which charges — which often escalate by tier — begin.
Worked example
A container posted available on Wednesday, 3 June 2026 with five working free days: the tool counts forward across working days only and returns Wednesday, 10 June — the fifth and last free day. Demurrage starts billing the next day, Thursday the 11th, so that is the date to plan the pickup against. Untick "Use business days" and the same five days run as straight calendar days: free time ends Monday, 8 June, and billing starts Tuesday the 9th — same container, same "5," two days apart.
Frequently asked questions
What date does the demurrage clock start from?
From the date the container becomes available for pickup — usually vessel discharge plus customs release, which the terminal publishes as the Last Free Day — not the day you were ready to collect it. Confirm that availability date with the terminal, because every downstream date depends on it.
Do free days count weekends and holidays?
It depends on the carrier's or terminal's tariff. Many count only working or gate-open days, which quietly extends your runway across a long weekend or port holiday; others count straight calendar days including weekends. None of the tariffs we checked moves the end of calendar-day free time to the next working day, so the calculator does not either unless you tick the extension box. Once free time ends, demurrage is usually billed on calendar days, weekends included. Four calendar free days from Tuesday 22 December 2026 end on Saturday 26 December; four working days on the US calendar end on Tuesday 29 December.
Is demurrage the same as detention, and is this advice?
No. Demurrage is for cargo left inside the terminal past free time; detention is a separate clock for keeping the carrier's container out too long before returning it empty. This tool tracks the demurrage start day only. It is general information, not legal or contractual advice — confirm any real charge against your bill of lading, the carrier's tariff, and the terminal.
What this calculator does not do
A limitation you know about costs far less than one you find after the deadline. These are the specific things this tool cannot work out for you.
- Calendar-day free time is counted straight through. A tariff that extends free time ending on a weekend or holiday is unusual; tick the box only if yours says so.
- Terminal gate closures on working days, which many tariffs exclude from free time, are not known to the tool; add them as custom holidays.
- Laytime and demurrage are contractual. The terms come from the charterparty or the carrier’s tariff, not from any statute, and the definitions of a running day, a working day and a weather working day differ between them.
Where these rules come from
The periods this calculator applies are taken from the primary sources below rather than from secondary summaries. Verify against them before relying on a date that matters.
- 46 CFR 541.6 (FMC demurrage and detention billing)
Invoices must state the allowed free time and its start and end dates; the rule does not set how free time is counted.
- Port of Los Angeles Tariff No. 4, Item 720
Free time is allowed “exclusive of Saturdays, Sundays and the legal holidays” unless the terminal opens its gates on those days.
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