How to Calculate Laytime and Demurrage Singapore 2026: NOR, Exceptions and Time‑bar Documents

Understanding how to calculate laytime and demurrage is essential for every party to a voyage charterparty calling at Singapore, one of the world’s busiest bunkering and transhipment hubs. Persistent port congestion, shifting berth availability and the near-universal reliance on Gencon and Shellvoy standard forms mean that disputes over laytime computation, Notice of Readiness (NOR) validity and demurrage time‑bars remain a significant source of commercial friction. This guide sets out, step by step, the practical methodology for laytime calculation in shipping, explains the critical rules governing NOR and the “once on demurrage, always on demurrage” doctrine, and provides worked examples, documentary checklists and Singapore-specific dispute-resolution pointers.

Whether you are a charterer’s operations team, a shipowner’s claims handler or in-house counsel preparing for a Singapore Chamber of Maritime Arbitration (SCMA) reference, the framework below is designed to be applied directly to live charterparty disputes.

Key Definitions, What Is Laytime and Demurrage?

Laytime

Laytime is the period of time agreed in a charterparty during which the shipowner makes the vessel available for loading or discharging cargo without additional charge. It is typically expressed as a fixed number of days or hours, for example, “7 weather working days, Sundays and holidays excepted” (SHEX) or “Sundays and holidays included” (SHINC). The precise formulation matters: a SHINC clause means every calendar day counts toward laytime, whereas a SHEX clause excludes Sundays and public holidays from the running total. Some charterparties adopt “weather working days” (WWD), under which laytime is suspended during periods when weather would have prevented cargo operations even if operations were not actually in progress.

Others use “unless used” (UU) riders, meaning excluded days count only if cargo work actually takes place.

Demurrage, Despatch and Detention

Demurrage is the liquidated damages payable by the charterer to the shipowner for each day (or part of a day) by which laytime is exceeded. It compensates the owner for the vessel’s detention beyond the contractually permitted period. The demurrage rate is stated in the charterparty, typically a fixed daily amount in US dollars. Despatch operates in the opposite direction: where the vessel completes cargo operations before laytime expires, the charterer may earn despatch money, usually at half the demurrage rate. Detention, by contrast, normally arises under contracts of carriage (such as container bookings) rather than charterparties, and relates to the late return of equipment rather than vessel time.

The distinction between detention vs demurrage is important because the contractual regimes, limitation periods and available remedies differ materially.

How Laytime Is Triggered and Stops, Notice of Readiness and Demurrage Rules

Valid NOR, Content, Recipients and Timing

Laytime does not begin to run simply because the vessel arrives. The shipowner (or master) must first tender a valid Notice of Readiness (NOR) to the charterer or its agent, confirming that the vessel has arrived at the agreed destination and is ready to load or discharge in all respects. The notice of readiness demurrage mechanism operates as a gateway: if the NOR is defective, laytime never starts, and no demurrage can accrue.

A valid NOR typically requires the following elements:

• Arrival. The vessel must have arrived at the contractual destination, the port, the berth or the customary waiting area, depending on whether the charterparty is a “port” or “berth” charter.
• Readiness. The vessel must be physically and legally ready to perform cargo operations: holds clean, gear operational, free pratique obtained and customs formalities cleared.
• Form and service. The NOR must be in writing and served on the correct party (charterer, agent, terminal) by the method specified in the charterparty (email, fax or telex). Oral notices are generally ineffective unless the charterparty expressly permits them.
• Timing. If the charterparty restricts the hours during which NOR can be tendered (e.g., “between 0600 and 1700 local time”), service outside those hours is premature and may be rejected.

Two abbreviations frequently appear in charterparty laytime clauses. WIBON (Whether In Berth Or Not) allows NOR to be tendered even if the vessel is waiting at anchorage because no berth is available. WIPON (Whether In Port Or Not) extends this further, permitting NOR to be tendered at a customary waiting place outside port limits. Both provisions significantly affect when laytime, and therefore potential charterparty demurrage in Singapore, begins to run.

Common NOR Pitfalls in Singapore Practice

Port restrictions at Singapore terminals can invalidate an otherwise correctly worded NOR. Operations teams should watch for:

• Pre-arrival inspection failures. If Maritime and Port Authority of Singapore (MPA) inspections or port state control detentions mean the vessel is not “ready in all respects,” any NOR tendered before clearance is premature.
• Berth congestion. Under a berth charter without a WIBON clause, the vessel must actually be at berth before laytime starts, congestion delays fall on the owner.
• Agent authority. Ensure the NOR reaches the party contractually entitled to receive it; serving notice on a terminal operator alone may be insufficient if the charterparty names the charterer’s local agent.

When Laytime Starts and Stops

After a valid NOR is tendered, most charterparties provide for a “turn time” or “notice time” before laytime actually commences, often six hours or the next working period. Laytime then runs continuously unless interrupted by an event the charterparty expressly excludes (rain, storms, holidays under a SHEX clause, strikes, or force majeure). Each interruption must be recorded in the Statement of Facts (SOF), signed by the master, agent and terminal. The SOF is the single most important contemporaneous document for any laytime and demurrage claim, without it, proving the precise start and stop times becomes extremely difficult in arbitration.

How to Calculate Laytime and Demurrage, Step‑by‑Step

The core algorithm for laytime calculation in shipping can be broken into five steps:

1. Identify the total laytime allowed under the charterparty (e.g., 5 days SHINC, or 120 running hours).
2. Determine the laytime commencement point (NOR tendered + notice time).
3. Record every start and stop of cargo operations, noting excluded periods (holidays, weather, strikes).
4. Sum total time used, subtracting excluded periods, to find actual laytime consumed.
5. Compare consumed laytime with allowed laytime: if consumed > allowed, the excess is demurrage time; if consumed < allowed, despatch may be earned.

Worked Example 1, Simple Bulk Cargo Discharge

Assume a Gencon charterparty for a bulk carrier discharging at a Singapore terminal. The charterparty allows 5 days SHINC (120 hours) for discharge. The demurrage rate is USD 15,000 per day. The vessel tenders a valid NOR at 08:00 on Monday 5 May 2026, with a 6-hour notice time, so laytime commences at 14:00 on 5 May.

In this example laytime is exactly exhausted at 14:00 on Saturday 10 May. Because the clause is SHINC, the rain stoppage on Thursday does not suspend laytime, Sundays, holidays and weather are all included. No demurrage is owed and no despatch is earned. Had discharge extended even one additional hour, the charterer would owe demurrage at USD 15,000 ÷ 24 = USD 625 per hour.

Worked Example 2, “Once on Demurrage” Scenario

Now adjust the facts. Suppose the vessel from Example 1 encounters an additional 18‑hour delay because the terminal suspends operations for a public holiday on Monday 12 May. Discharge does not complete until 08:00 on Monday 12 May, 18 hours beyond the expiry of allowed laytime.

Total demurrage time: 42 hours. At USD 15,000 per day (USD 625 per hour), the charterer owes USD 26,250. The public-holiday closure does not interrupt demurrage because, under the widely applied principle of “once on demurrage, always on demurrage,” exceptions that would otherwise suspend laytime (such as holidays or weather) cease to apply once laytime has expired, unless the charterparty contains an express clause to the contrary.

Operations teams looking for a ready-made laytime calculation Excel template, or a laytime and demurrage PDF checklist, can find free downloadable tools from providers such as Heisenberg Shipping’s online laytime calculator, which automates SHINC, SHEX and weather-day adjustments.

Demurrage Charging, Pro Rata Calculations and Billing

Demurrage is charged at the daily rate specified in the charterparty. Where the excess time is less than a full day, the convention is to calculate pro rata to the hour and minute. For example, if the demurrage rate is USD 15,000 per day and the vessel is detained for 3 days, 7 hours and 30 minutes beyond laytime expiry, the calculation is:

• 3 full days: 3 × USD 15,000 = USD 45,000
• 7 hours 30 minutes: (7.5 ÷ 24) × USD 15,000 = USD 4,687.50
• Total demurrage: USD 49,687.50

Interest on late-paid demurrage may also accrue, depending on the charterparty terms or the governing law. Under English law, which governs most Gencon and Shellvoy forms, demurrage carries interest from the date it falls due. The shipowner should issue a demurrage invoice promptly, supported by the NOR, SOF, cargo documents and a clear time calculation. Delays in invoicing risk triggering contractual time‑bar clauses and may weaken the claim in arbitration.

Detention vs Demurrage, Who Pays?

Exceptions and Special Rules, “Once on Demurrage, Always on Demurrage”

The doctrine of “once on demurrage, always on demurrage” is one of the most consequential rules in charterparty disputes. It means that once laytime has been fully consumed and the vessel is on demurrage, time continues to count against the charterer even during events (weekends, holidays, bad weather, strikes) that would otherwise have interrupted laytime. The rationale is straightforward: demurrage is a form of liquidated damages for breach, and once the breach has occurred, subsequent delays, regardless of their cause, do not pause the accrual.

However, this is a default position, not an absolute rule. The charterparty can, and sometimes does, expressly provide that certain exceptions continue to apply even after laytime expires. For instance, some amended Gencon forms include a rider clause stating that “time lost due to force majeure shall not count as demurrage.” Where such language is present, demurrage will be interrupted by the specified event. Industry observers expect that parties trading into congested ports like Singapore are increasingly negotiating bespoke exception clauses, particularly where terminal closures are foreseeable.

Practical Checklist to Rebut “Once on Demurrage” Claims

If you are a charterer defending against a demurrage claim that relies on this doctrine, gather the following evidence:

• Charterparty rider clauses. Check whether any amendment or addendum carves out specific events from the “once on demurrage” default.
• NOR validity. If the original NOR was defective, laytime may never have validly commenced, meaning the vessel cannot be “on demurrage” at all.
• Fault of the shipowner. Where the delay after laytime expiry is caused by the shipowner’s own act or default (e.g., equipment breakdown, crew issues), many arbitral tribunals, including those convened under SCMA, will not allow demurrage to run for that period.
• Express contractual interruptions. Some charterparties provide that laytime and demurrage are to be calculated on the same time-counting basis, effectively carrying SHEX or weather exclusions through into the demurrage period.

When Laytime Stops, Common Events and Who Bears Risk

Documentary Time‑Bars, What to Serve, by When, and Demurrage Time Bars Explained

Demurrage time bars are among the most litigated provisions in shipping. A time‑bar clause requires the shipowner to present its demurrage claim, supported by specified documents, within a fixed period after completion of discharge. Failure to comply means the claim is extinguished, regardless of its merits. Charterparty demurrage in Singapore arbitration is frequently defeated on time‑bar grounds alone, making documentary discipline critical.

Under the Gencon 1994 form, the standard time‑bar provision requires the demurrage claim to be supported by “all available supporting documents” and submitted within 90 days of completion of discharge. Shellvoy 6 imposes a stricter requirement: the claim and supporting documents must be received within 90 days. Amended charterparties may shorten this period to as little as 30 days.

Best practice is to serve the claim and documents by the method specified in the charterparty (email with read receipt, registered mail, or through the broker). Retain proof of service: in SCMA proceedings, the tribunal may require evidence that the claim was received, not merely sent. Notify your P&I club immediately upon any delay to laytime, early notification ensures the club can assist with evidence preservation and claim preparation.

Dispute Routes in Singapore, SCMA, LMAA, Courts and Enforcement

Singapore is a leading seat for maritime arbitration, and charterparty demurrage in Singapore is most commonly resolved through the SCMA or, where the charterparty so provides, under London Maritime Arbitrators Association (LMAA) terms with London as the seat. The choice of forum is determined by the arbitration clause in the charterparty, Gencon 1994, for instance, offers a tick-box choice between London, New York and a third option the parties may fill in.

Key practical considerations for Singapore-seated disputes include:

• SCMA Rules. The SCMA Arbitration Rules provide for expedited procedures for claims below USD 150,000, with a sole arbitrator and a streamlined timetable, well suited to straightforward demurrage disputes.
• Interim relief. Singapore courts may grant interim injunctions or orders for security under the International Arbitration Act, even where the arbitration is seated elsewhere.
• Enforcement. Singapore is a signatory to the New York Convention, meaning SCMA awards are enforceable in over 170 jurisdictions. This makes Singapore a strategically advantageous seat for owners seeking to enforce demurrage awards against charterers with assets abroad.
• Costs. SCMA arbitration costs are generally competitive compared to LMAA London proceedings, particularly for smaller claims.

Practical Toolkit, Templates and Checklists for Laytime Calculation

Effective laytime and demurrage management depends on systematic documentation from the moment the vessel arrives at the loading or discharge port. The following toolkit items, available as downloadable resources, are designed to support claims handlers and operations teams:

• Sample NOR wording. A model Notice of Readiness template incorporating WIBON/WIPON language, addressee fields and timing provisions aligned with Gencon 1994 and Shellvoy 6 requirements.
• Statement of Facts (SOF) checklist. A step-by-step form listing every event to be recorded (NOR tendered, laytime commenced, weather interruptions, hatch openings, completion of operations) with signature blocks for master, agent and terminal.
• Laytime calculation Excel template. A downloadable spreadsheet automating SHINC, SHEX and “unless used” calculations, with built-in demurrage and despatch outputs. Free online tools such as the Heisenberg Shipping laytime calculator also provide browser-based alternatives for quick checks.
• Demurrage invoice template. A standard-form invoice setting out the time calculation, rate, total amount and supporting document index, formatted for submission within charterparty time‑bar deadlines.

These resources can be adapted to the specific charterparty form in use. For bespoke review of time‑bar compliance or NOR validity under Singapore law, specialist shipping litigation counsel should be consulted.

Conclusion and Next Steps

Knowing how to calculate laytime and demurrage accurately, and how to preserve the documentary record that supports a claim, is the single most effective way to protect your commercial position in a voyage charterparty. The key takeaways are straightforward: verify NOR validity before assuming laytime has started, record every event in a signed SOF, understand whether your charterparty operates on SHINC, SHEX or weather-working-day terms, and submit your claim with full supporting documents well inside the time‑bar deadline. For Singapore-seated disputes, the SCMA’s efficient arbitration framework offers a cost-effective route to resolution.

Early engagement of specialist shipping litigation counsel, particularly for complex “once on demurrage” scenarios or contested NOR validity, remains the most reliable way to secure or defend a demurrage position.

Sources

1. Singapore Chamber of Maritime Arbitration (SCMA), A Snapshot Guide to Laytime & Demurrage
2. Shipowners’ Club, Laytime & Demurrage Publication
3. HandyBulk, Laytime Calculation Examples
4. Veson (IMOS), Laytime Calculation Help
5. Fortior Law, Laytime and Demurrage Explainer
6. Maritime and Port Authority of Singapore (MPA)
7. ClearVoyage, Difference Between Laytime and Demurrage
8. Heisenberg Shipping, Online Laytime Calculator