Boat ETA from Speed Calculator

It applies the direct nautical relationship between knots and nautical miles, then reports the UTC arrival timestamp and the journey duration. Use it for passage planning, arrival updates, marina coordination, or quick scenario comparisons whenever a steady-speed estimate is appropriate.

Enter distance, speed over ground, and departure time

Start with the distance that remains along the route, expressed in nautical miles. Use route distance rather than a straight line between two coordinates when hazards, channels, traffic separation schemes, or planned waypoints make the sailed track longer. Next, enter speed over ground in knots. Speed over ground is the useful value here because it already reflects the vessel's progress relative to the earth; speed through the water can produce a misleading ETA when current is present. Finally, provide the departure time as an ISO-8601 timestamp with either Z for UTC or an explicit offset such as +02:00. Requiring an offset removes the ambiguity created by local clock times and daylight-saving changes. The calculator normalizes that timestamp to UTC before adding the computed duration. A distance of zero is valid and returns the normalized departure instant as the arrival time, while speed must always be greater than zero because no finite ETA can be calculated without forward progress.

Understand the calculation and its precision

The calculation uses the definition of a knot: one nautical mile per hour. Travel time in hours is therefore the remaining nautical miles divided by speed over ground in knots. For example, a vessel with 42.5 nautical miles remaining at 8.5 knots has a travel time of exactly five hours. The tool converts the result to seconds and rounds to the nearest whole second before adding it to the departure timestamp, because the returned arrival time is displayed at one-second precision. It also returns decimal travel hours, total travel seconds, and separate hour, minute, and second components so the same answer is convenient for logs, interfaces, and downstream automation. All calendar arithmetic is deterministic and independent of the current clock. The calculator does not silently assume a time zone, consult live vessel data, or change speed during the trip. Identical inputs always produce an identical result, which makes the endpoint suitable for repeatable planning calculations and automated checks.

Treat the result as a steady-speed planning estimate

A computed ETA is only as reliable as the inputs and assumptions behind it. This calculator holds speed over ground constant for the entire remaining distance. Real passages rarely do that perfectly: wind, sea state, tidal streams, river current, traffic, visibility, sail changes, speed restrictions, locks, bridges, fuel stops, and maneuvering near the destination can all change the arrival time. Recalculate whenever the distance-to-go or observed speed changes materially, and add an operational buffer when coordinating a berth, pilot, launch, pickup, or crew handover. For a useful rolling estimate, take distance-to-go and speed over ground from the same navigation source at the same moment. Very low speeds can create extremely long theoretical durations, so confirm that the vessel is actually making meaningful progress toward the destination rather than drifting sideways or waiting. This result supports planning and communication; it does not replace a passage plan, official navigation information, watchkeeping judgment, or the skipper's assessment of conditions.