Estimate how long a passage will take, when you’ll arrive, and a conservative arrival that builds in a safety margin. Enter the distance, your average speed, and your departure time.
Passage Time Calculator
Estimate how long a passage will take, when you will arrive, and a conservative arrival with a safety margin.
Estimated duration
12h 0m
12.0 h
Estimated arrival
21:00
same day
With 20% safety buffer
How it works
The estimate is straightforward: divide the distance by your average speed to get the time, then add it to your departure to get the arrival.
duration = distance ÷ average speed • arrival = departure + duration
The safety buffer then adds a margin to the duration, so the "conservative arrival" reflects a slower-than-planned passage. Aim to plan around that later time, especially when arriving before dark or catching a tide matters.
Limitations & good practice
- It assumes a constant average speed. Real speed rises and falls with wind, current and sea state. Feed it a realistic route average, not your best surfing speed.
- Average speed means speed made good. Tacking, leeway and detours mean your speed through the water must be higher than the straight-line average this tool uses.
- It does not model tides or currents over time. A favourable or foul tide that changes during the passage can shift the real arrival by hours — plan tidal gates separately.
- Departure is treated as local clock time. Arrival is shown on the same clock with a day count; it does not account for crossing time zones on a long passage.
- The buffer is a flat percentage. It is a planning cushion, not a route-specific risk model. Increase it for unfamiliar waters, night arrivals or a hard tidal deadline.
Treat the result as a planning estimate, re-check it underway against your actual progress, and always leave a float plan ashore with your expected arrival.