Waypoint Dead Reckoning Calculator
Calculate your estimated position from a known starting point using heading, speed, and elapsed time.
Works on land, sea, and air.
Dead reckoning is the process of estimating your current position by starting from a known location and applying your direction of travel and distance covered. It is one of the oldest navigation techniques, used for centuries before GPS by sailors, pilots, and explorers.
The formula uses basic trigonometry:
- New latitude = Start lat + (distance × cos(heading)) / 111.32
- New longitude = Start lon + (distance × sin(heading)) / (111.32 × cos(start lat))
Where 111.32 km is the approximate length of one degree of latitude, and the longitude correction accounts for the fact that degrees of longitude get shorter as you move away from the equator.
Distance = Speed × Time (always, in any consistent units)
Sources of error in dead reckoning:
- Speed error — your actual speed may differ from your estimated speed (current, wind, terrain)
- Heading error — a 1° heading error at 100 km = 1.75 km off course
- Accumulated error — each error compounds with the next, so DR position drifts over time
- Leeway (marine/aviation) — wind and current push you sideways off your heading
This is why navigators historically “fixed” their position at every opportunity — using landmarks, celestial observations, or radio beacons — and then resumed dead reckoning from the new known position.
Modern use: Despite GPS, dead reckoning remains essential. Submarines use inertial navigation (sophisticated DR). Aircraft use it as a backup. Hikers use pace counting and compass bearings. Autonomous vehicles use DR between GPS updates.
Tip: For short distances (under 100 km), this flat-Earth approximation is accurate to within 0.1%. For longer distances, use the spherical formula.