Work out an arrival time from a planned speed, or the speed needed to make a given arrival. This voyage and ETA calculator computes everything in UTC and reports the answer in both UTC and the arrival port’s local time, so there is no ambiguity when you pass it to the agent or the pilot station.
Work out an arrival time from a planned speed, or the speed needed to make a given arrival. All times are computed in UTC and shown in both UTC and local time.
Departure
Required arrival
A planning estimate. Passage time in service depends on weather, current, hull condition and traffic; always work to the passage plan and the master's standing orders.
How to calculate ETA from distance and speed
Passage time. Divide the distance to go in nautical miles by the speed in knots. That gives the time in hours, because a knot is one nautical mile per hour. A 2,400 mile passage at 12 knots is 200 hours, which is 8 days and 8 hours.
Arrival time. Add the passage time to the moment of departure. Do the addition in UTC, not on the ship’s clock — a vessel crossing zones retards or advances its clocks during the passage, so a departure time and an arrival time taken from the bridge clock are not on the same scale. Convert to the arrival port’s offset only at the end, for display.
Standby time. Manoeuvring out of the berth, waiting for a pilot or drifting off the fairway is not run at sea speed, so keep it out of the distance-over-speed sum and add it to the total separately. Folding it in distorts both the passage time and any fuel figure you take from it.
Weather margin. A percentage added to the passage for head winds, adverse current, hull fouling or canal delay. In ETA mode it pushes the arrival later; in required-speed mode it reserves part of the window so the speed you get back still carries a buffer.
Working backwards: the speed required to make an arrival
The more useful question in practice is usually the other way round. You have a laycan, a berthing window or a tidal gate, and you need to know what speed makes it. Take the hours between departure and the required arrival, subtract standby time, and divide the distance by what remains.
Switch the calculator to Calculate required speed and it does that, showing how the window is consumed line by line. If the answer comes back above about 25 knots it says so, because that is beyond the service speed of virtually every merchant ship and normally means the distance or the window is wrong rather than the ship being slow.
Why ETA should always be given in UTC as well as local time
This is the error that causes the most confusion in practice, and it costs money when a berth or a tide is missed. A ship keeps a clock on an offset the master sets, and that offset changes during a passage across zones. Quote a local arrival time alone and the receiver has to guess which local time you meant. Quote UTC alongside it and there is nothing to guess.
For the same reason this calculator uses fixed UTC offsets rather than named time zones. Named zones carry shore daylight saving rules, and applying those to a vessel at sea introduces an hour of error that is very hard to spot afterwards. Set the offset the clock is actually on.
Then work out the bunkers
Once you have the time underway, the fuel follows from it. The ship fuel consumption and CO₂ calculator takes days at sea and gives you tonnes required and carbon dioxide produced, for the main engine and the auxiliaries separately. The button in the results above carries the calculated days straight across.
Voyage and ETA calculator FAQs
How do you calculate ETA from distance and speed?
Divide the distance in nautical miles by the speed in knots to get the passage time in hours, then add that to the time of departure. A 2,400 mile passage at 12 knots takes 200 hours, or 8 days and 8 hours, so a noon departure arrives at 2000 hours eight days later. Add any pilot and standby time separately, because that is not run at sea speed.
What speed do I need to make a given arrival time?
Take the hours between departure and the required arrival, subtract any standby time, then divide the distance by the hours that are left. Switch this calculator to "Calculate required speed" and it does exactly that, and it warns you when the answer comes out above about 25 knots, which is beyond most merchant ships and usually means the distance or the window is wrong.
Why should ETA always be given in UTC as well as local time?
Because a ship crossing zones changes its clocks during the passage, so a local time on departure and a local time on arrival are not on the same scale. UTC does not move. Give both, and there is no ambiguity for the agent, the pilot station or the charterer — which is why this calculator always shows the two together.
Does this calculator handle daylight saving time?
It works in fixed UTC offsets rather than named time zones, deliberately. A ship keeps a clock on an offset that the master sets, not on a shore location with its own summer time rules, and applying shore daylight saving to a vessel at sea causes an hour of error that is hard to spot. Set the offset the clock is actually on, both for departure and for the arrival port.
What is a weather or delay margin?
It is a percentage added to the calculated passage time to allow for head winds, adverse current, hull fouling, traffic or canal delays. In ETA mode it pushes the arrival later. In required-speed mode it works the other way, reserving part of the window so the speed you get back still leaves a buffer.
Should pilot and standby time be part of the passage?
No, keep it separate. Manoeuvring at reduced revolutions in and out of port, waiting for a pilot or drifting off the fairway are not run at sea speed, so folding them into a distance-over-speed calculation distorts both the passage time and any fuel figure derived from it. Enter them in the standby field and they are added to the total without affecting the sea passage.
Part of the marine engineering calculators on this site — sea service, bunkers and emissions, and passage planning.