Free tool
Enter your departure and arrival times exactly as the boarding pass shows them, each in its own local time. We convert both to a single timeline and give you the true air time, the distance, and what your body clock will read when the wheels touch down.
True flight time
12h
London to Tokyo · 9,559 km great-circle
Flying east, the destination clock is 8h ahead. So a 12h flight appears to take 20h on the wall. When you land, your body still thinks it is 22:00 back in London.
A boarding pass shows two local times: when you leave and when you land, each on the clock of its own city. Subtract one from the other and you get a number that has nothing to do with how long you were actually in the air. The gap hides, or invents, the difference between the two time zones. Fly London to Tokyo and the clock claims twenty hours; the plane was up for roughly twelve. The other eight are simply Japan being ahead.
The fix is to put both times on one timeline. We anchor each local time to its city's IANA zone, convert both to the same universal instant, and subtract those. What is left is the real elapsed time — the figure that decides whether you make a connection, not the one the wall clock teases you with.
Direction changes the illusion. Flying east, into a clock that runs ahead, the trip looks longer than it was: you lose hours on paper even though the flight was ordinary. Flying west, chasing the sun, the clock barely moves or even runs backwards — a transatlantic hop can land "earlier" than it left. The air time is identical in both directions for the same route; only the arithmetic on the clock flips. The body-clock reading below tells you what your internal time still thinks it is, which is the better predictor of jet lag than any departure board.
The distance we show is the great-circle distance: the shortest path over the curve of the Earth between the two cities, computed with the haversine formula. Real flight paths wander for wind, airspace, and traffic, so the figure is a clean lower bound rather than the exact track. It is enough to sanity-check a duration — a 12-hour reading over 9,500 km is plausible, the same 12 hours over 1,000 km is not. For a side-by-side of two cities' clocks and overlap windows, the time zone converter picks up where this leaves off.