How ETA Works

PortReckon estimates a vessel's transit time and arrival from three inputs: the sea distance between your ports, the ship's speed, and any slowdown or delay you add. This page explains how that estimate is built.

Distance

The route follows real shipping lanes between your origin, an optional waypoint, and the destination, and its length is measured in nautical miles (nmi). One nautical mile equals 1.852 km, so the distance is also shown in kilometres. If no sea lane is found, the tool falls back to a straight-line (great-circle) estimate.

Speed

Speed is entered in knots, where one knot is one nautical mile per hour. Because a nautical mile is 1.852 km, the app shows a live km/h value next to the field. The default planning speed is 16 knots, a typical figure for a loaded merchant vessel.

The core formula

At its simplest, transit time is distance divided by speed, plus any fixed delay:

transit hours = distance (nmi) / effective speed (knots) + fixed delay (hours)

The effective speed is your entered speed reduced by the total slowdown percentage, so a slower ship takes proportionally longer.

Slowdown and delay factors

Real voyages rarely run at full speed the whole way. The tool offers preset factors that each add to your slowdown percentage:

You can also set a manual slowdown percentage and a fixed delay in hours (for example, time spent waiting for a berth). These combine into the effective speed and the final ETA.

What the result means

The output is an estimate for planning and comparison, useful for weighing one route or speed against another. It is not a guaranteed schedule, and it does not account for live weather, traffic, or port operations.

Routes are for planning/visualization only and are not certified for navigation.