How is laytime allowed calculated?

Laytime allowed is the cargo quantity divided by the agreed handling rate in tonnes per day, summed across loading and discharging ports. For example, 30,000 tonnes loaded at 10,000 t/day allows 3 days for loading, plus the discharge allowance.

What is the difference between demurrage and despatch?

If the ship is detained beyond the allowed laytime, the charterer pays demurrage at the agreed daily rate for the extra time. If cargo work finishes early, the owner often pays despatch for time saved, conventionally at half the demurrage rate.

Why is despatch usually half of demurrage?

Despatch at half demurrage (DHD) is a long-standing charter-party custom: the owner shares the benefit of fast cargo work but at a lower rate than the penalty for delay. The exact ratio is whatever the charter party specifies, so always check the clause.

What is the difference between lumpsum and per-tonne freight?

Lumpsum freight is a fixed sum for the whole voyage regardless of cargo loaded, shifting quantity risk to the charterer. Per-tonne freight multiplies an agreed rate by the cargo quantity actually carried, so freight rises and falls with the loaded tonnage.

What is the Charter Party Freight Calculator?

Computes voyage-charter freight (lumpsum or rate per tonne times cargo), then works out laytime allowed from cargo and load/discharge rates, compares it with time actually used, and returns demurrage owed or despatch earned. Built for chartering managers and shipbrokers preparing settlement. It runs free in your browser on Gera Tools, with nothing uploaded.

Charter Party Freight Calculator

Name: Charter Party Freight Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Get one useful tool a week

Like this tool? Enter your email and we'll send you one genuinely useful Gera tool a week — plus a link to come back to this one. No spam, one-click unsubscribe any time.

Settling a voyage charter means agreeing two numbers: the freight earned for carrying the cargo, and the demurrage or despatch arising from how fast that cargo was loaded and discharged. This calculator does both from the charter-party terms.

How it works

Freight is either a fixed lumpsum or a rate times the cargo loaded. Laytime allowed is the cargo divided by the agreed handling rate; comparing it with time actually used gives demurrage or despatch:

freight         = lumpsum   OR   rate_per_tonne × cargo_tonnes
laytime_allowed = cargo / load_rate + cargo / discharge_rate   (days)
time_used       = load_time + discharge_time                   (days)

if time_used > allowed:  demurrage = (used − allowed) × demurrage_rate
if time_used < allowed:  despatch  = (allowed − used) × despatch_rate

Despatch is conventionally paid at half the demurrage rate (despatch half demurrage, or DHD), but the charter party governs the exact figure.

Worked example

For 30,000 tonnes at $25 per tonne, freight is $750,000. Loading at 10,000 t/day and discharging at 15,000 t/day allows 3 + 2 = 5 days of laytime. If the ship actually used 6 days total, the charterer owes one day of demurrage; at a $20,000/day rate that is $20,000. Had cargo work finished in 4 days, the owner would pay one day of despatch at the half rate — $10,000.

Reversible versus non-reversible laytime

The calculator totals loading and discharging time together, which is equivalent to reversible laytime — time saved at one port offsets time lost at another, and only the net difference counts. This is the most charterer-friendly arrangement.

Under non-reversible terms, each port’s laytime is counted and settled separately. If a vessel finishes loading in 2 days against a 3-day allowance but takes 3.5 days to discharge against a 2-day allowance, the charterer owes half a day of demurrage at the discharge port regardless of the half-day saved at load. For non-reversible calculations, run each port through the tool independently rather than combining them.

Practical guidance for chartering managers

Verify the laytime commencement clause before counting. Laytime does not always start the moment a vessel arrives. Most charter parties require a Notice of Readiness (NOR) to be tendered by the master and accepted — often with a waiting period of 6 or 12 hours before laytime begins. Failing to count correctly from NOR acceptance is one of the most common disputes in voyage-charter settlements.
Check weather and holiday exceptions. SHINC (Sundays and Holidays Included), SHEX (Sundays and Holidays Excepted), and WIBON/WIPON clauses all affect how counting runs. The tool computes uninterrupted running time — annotate any excluded periods separately if your charter party specifies them.
Demurrage rates are daily, but time can be fractional. Half a day of overrun at $20,000/day produces a demurrage claim of $10,000. Fractions accumulate per hour or part-hour, so precision matters on long port calls.
Freight and laytime settlement are usually calculated independently. Freight is normally earned on shipment (or delivery), while demurrage is settled after completion of cargo operations. Make sure the handling rates and the demurrage rate come straight from the charter party, and confirm whether laytime is reversible before netting load and discharge time.