Reversible Laytime Calculator: Multi-Port Pooling

Formula, assumptions, and limits

Reversible laytime is a single pooled allowance covering every loading and discharging call of the voyage. To calculate it, add each call’s used hours from its statement of facts, subtract the pooled allowance, and price the net at the daily rate divided by 24:

t_used,i - laytime used at call i, from that port’s statement of facts with the charter’s counting rules applied. T_allowed - the single pooled allowance the charter grants, here in hours. r_dem / r_des - daily demurrage and despatch rates, divided by 24 to price hours.

“Reversible” and “all purposes” both produce a pooled comparison, with a drafting difference worth respecting: reversibility is classically an option to pool separate load and discharge allowances, while all purposes grants one undivided allowance outright. The BIMCO Laytime Definitions 2013 define the reversible option; “all purposes” is established trade usage outside the Definitions. Either way, the aggregation is the easy part; each port’s used figure still has to be built on its own SOF, with notice, commencement, and exception rules applied per call, before it earns its place in the sum.

Limits: the calculator prices the net at one demurrage rate, the common case. Charters that escalate the rate (higher after a stated period on demurrage) or split rates by port need the net split by hand before pricing. And the once-on-demurrage point matters operationally on long itineraries: after the pool runs out mid-voyage, later calls count their time gross of exceptions, which inflates used figures a desk might otherwise expect the exceptions to trim.

How to use this calculator

1. Enter the total laytime allowed across all ports, in hours, from the charter party.
2. Add a row per call and enter each port’s used time from its statement of facts.
3. Enter the demurrage rate, and the despatch rate where agreed.
4. Read the total used, the net in hours and days, and the USD settlement; the chart shows which call spent the pool.

Building each call’s used figure

The pooled comparison is only as good as its inputs, and each input is a small laytime statement of its own. At every call the clock starts when the charter says it does: notice of readiness validly tendered, the notice time run, and any berth-or-port conditions satisfied. It then counts under the charter’s terms, weather working days, SHINC or SHEX, with each port’s own weather, holidays, and interruptions applied to that port’s facts. Shifting time, waiting for berth, and stoppages attributable to the owner are the usual contested entries.

Reversibility adds one cross-call wrinkle: once the pool is exhausted, the voyage is on demurrage, and time at every later call counts gross of the exceptions that would otherwise have trimmed it. A desk that builds each call’s figure as if the pool were fresh will understate the used total on the back half of a long itinerary, which flatters the charterer until the recount.

Worked example

A reversible charter allows 120 hours all purposes across four calls. The statements of facts yield 35, 28, 45, and 20 hours used: 128 hours total, 8 hours over the pool. At USD 24,000 per day demurrage, the voyage owes 8/24 × 24,000 = USD 8,000. Had the last port used 10 hours instead, the voyage would have finished 2 hours inside the pool and earned 2/24 × 12,000 = USD 1,000 despatch at the half rate. One slow call out of four decides the whole settlement, which is the reversible bargain in one sentence: every port shares one clock.

What the pool does to operations

A shared clock changes behavior before it changes money. Operators on reversible fixtures spend the pool deliberately: pushing the cheap, fast port hard to bank hours the congested port will burn, accepting a waiting berth at one call because the pool still holds, and watching the aggregate the way a per-port fixture never requires. The running total this calculator maintains is the figure that should sit in the voyage file after every call, because the moment it crosses the allowance, every later hour is demurrage money and the counting rules loosen in the owner’s favor.

Common errors

1. Comparing per port on a reversible fixture. The whole point of the pool is that port-level overruns do not exist; only the aggregate settles. Running per-port math on a reversible charter invents demurrage at fast-then-slow itineraries.
2. Pricing hours at the daily rate. Rates are per day; an 8-hour net is a third of a day, not 8 days. The divide-by-24 lives in the formula for exactly this reason.
3. Counting one port’s time under another port’s rules. Each call’s used figure is built on its own SOF and the same charter terms; a holiday that did not count at the load port does not retroactively count because the discharge port was slow.
4. Forgetting the option is the charterer’s. Where reversibility is optional, the charterer elects after the figures are known; an owner’s settlement that assumes the basis the owner prefers will not survive the election.

About This Reversible Laytime Calculator

Four statements of facts arrive from four agents in four formats, and the settlement turns on an aggregate nobody computed during the voyage. That is the normal condition of a multi-port reversible fixture, and the reason this page keeps a running pool. Built for owners, charterers, and operators on reversible or all-purposes fixtures, it takes the pooled allowance, a row per call with that port’s used time, and the two rates, and returns the net in hours and days with the USD result.

The aggregation follows the reversible convention the BIMCO Laytime Definitions describe, pricing the net at the daily rates pro rata by the hour. Per-call counting stays where it belongs, on each port’s SOF under the charter’s terms; the two-port settlement with the per-port versus reversible comparison lives in the laytime and demurrage calculator, and the claim the result becomes must beat the charter’s time bar.

The chart draws each call’s used hours beside the voyage total and the pooled allowance, so the slow call that spent the pool stands out, and the table fallback carries the same figures for the file.

Further reading

• Reversible laytime and despatch
• Laytime
• Demurrage
• Laytime and demurrage calculator
• Demurrage time bar calculator

Frequently asked questions

How does reversible laytime work across multiple ports?

The charter grants one pooled allowance for all loading and discharging calls instead of a figure per port. Each port's used time, counted on its own statement of facts, aggregates into one total; the voyage is on demurrage only when the pool is exhausted, and time saved anywhere offsets time lost anywhere.

Who benefits from reversible laytime?

Usually the charterer, which is why reversibility is commonly drafted as the charterer's option. A fast load port banks time the discharge port can spend, and the option is exercised after the figures are known, whichever way settles cheaper.

When does demurrage start on a reversible charter?

When the pooled allowance is exhausted, wherever the ship then is. From that point the once-on-demurrage principle generally applies for the remainder of the voyage's cargo operations, and laytime exceptions stop protecting the charterer unless the charter says otherwise.

Is used time counted differently at each port?

Each port's clock runs on its own facts and the same charter terms: notice of readiness, commencement rules, and counting exceptions apply per call. Reversibility changes only what the aggregated total is compared against, not how any port's time is counted.