Free tool
Flight duration calculator
Enter departure and arrival times in their local time zones to see elapsed flight time, great-circle distance, and the body-clock time when you land.
True flight time
12h
London to Tokyo · 9,559 km great-circle
- Clock says
- 20hon the wall
- Time-zone shift
- 8h east
- Body clock on arrival
- 22:00
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.
The default route, worked through
Open the calculator and it loads a London to Tokyo example: departure at 10:00 on 1 June, arrival at 06:00 on 2 June. Subtract the wall clocks and you get 20 hours. In June, London runs on British Summer Time at UTC+1 while Japan stays on UTC+9 all year, so eight of those hours are pure zone offset. Take them away and the true elapsed figure is 12 hours. The great-circle distance between the two cities is about 9,560 km, which makes a 12-hour reading entirely plausible. The body-clock readout completes the picture: landing at 06:00 Tokyo time, your internal clock still reads 22:00, late evening, which is exactly the mismatch the first day of a long eastbound trip is famous for. Every result on this page is built from those same three moves: anchor, convert, subtract.
Why the clock lies about flight length
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.
Eastbound vs westbound on the clock
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.
Great-circle distance, briefly
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.
Landing before you took off
Westbound crossings of the International Date Line produce the strangest tickets in aviation: leave Tokyo in the evening and touch down in North America on the afternoon of the same calendar day, hours before the printed departure. Nothing paradoxical happened; the flight simply out-ran the calendar boundary. Because this calculator converts both entries to instants on a single timeline before subtracting, date-line itineraries come out with the correct positive duration. The only thing to watch is the date field: enter each date exactly as the ticket prints it for its own city, even when the arrival date looks earlier than feels right. If the two instants end up reversed, the tool shows a warning rather than a negative number, which almost always points to a missing next-day date.
Getting trustworthy numbers in
- Copy times straight from the booking or boarding pass, each in its own city's local time. Never pre-convert anything yourself; that is the calculator's job.
- Watch for the small +1 next to arrival times in timetables. It means the landing is on the following calendar day, so the arrival date field needs to move forward by one.
- Remember that published times are gate to gate. The result is scheduled block time, the figure that matters for connections, not the shorter airborne segment.
- Sanity-check against the distance. Long-haul cruise speeds mean a 1,000 km hop should not read anywhere near 12 hours; if it does, a date or an AM/PM entry has slipped.
Flight time questions
Does the result include taxi time?
That depends on the times you enter. Airline timetables publish gate departure and gate arrival, so entering those gives you scheduled block time, which includes taxiing at both ends. The airborne portion is somewhat shorter.
Why is my return flight scheduled longer than the outbound?
Prevailing winds at cruising altitude, especially the jet streams, usually favour one direction. Eastbound crossings of the North Atlantic and North Pacific are typically scheduled shorter than the westbound return over the same route.
Is the distance shown the route the plane actually flies?
No. It is the great-circle distance, the shortest surface path between the two cities. Real tracks bend around weather, winds, and airspace restrictions, so the flown distance is somewhat longer.
How are daylight saving changes handled?
Each local time is resolved through its city's IANA timezone rules for the exact date entered, so a flight that spans a clock change is still measured correctly on the shared timeline.
Why do I see a warning instead of a duration?
The arrival you entered lands at or before the departure once both are placed on one timeline. The usual cause is a missing next-day date on an overnight flight; a few routes also cross the date line.