What the Flight Time Calculator does
This calculator works out how long a flight really lasts from the local departure and arrival times printed on a ticket, or the local arrival time from a departure time and a duration, by converting both ends through their time zones. Date lines, daylight-saving changes and half-hour zones are handled by the IANA time-zone rules built into your browser.
Pick the two airports as well and it adds the great-circle distance between them and the average speed the timetable implies - a quick way to spot a wrong date or time zone before you plan a connection or a pickup.
How to use it
- Choose what you want: the flight duration (you know both local times) or the arrival time (you know the departure and how long the flight takes).
- Set the departure time zone and local departure date and time, exactly as the ticket shows them. Tickets always use local time at each airport.
- Set the arrival time zone and either the local arrival date and time or the duration in hours and minutes.
- Optionally type an airport code or city in each airport box and pick from the list to add the distance. Airports only supply coordinates; the time zones stay as you set them.
- Read the duration, the clock difference and the calendar change, and check the timeline, which shows both events in both zones and in UTC.
Reading the results
Duration is the difference between two instants, so it is correct even when the clock at the destination shows an earlier time than when you left. Airlines publish block time - gate to gate, including taxiing - not time in the air.
The destination clock line says how far the arrival zone's clock is from the departure zone's on the day you land. That is the number you set your watch by, and the starting point for a jet-lag plan.
A calendar change of -1 day is normal eastbound across the International Date Line in the Pacific; +1 or +2 days is normal on long westbound overnight flights. If the average speed is above about 1,100 km/h or below 150 km/h, check the zones and dates.
Worked example: London Heathrow to New York JFK on the first day of UK summer time
A ticket shows departure 09:00 on 30 March 2025 from London and arrival 11:40 the same day in New York. UK clocks went forward at 01:00 UTC that morning, so 09:00 in London is 08:00 UTC. New York had changed on 9 March and was at UTC-4, so 11:40 there is 15:40 UTC.
The flight therefore lasts 15:40 - 08:00 = 7 hours 40 minutes, even though the clocks differ by only 2 hours 40 minutes. New York is 5 hours behind London that day.
Heathrow and JFK are 5,555 km apart on the great circle, so the timetable implies an average of 5,555 / 7.667 = about 725 km/h gate to gate - realistic for a westbound Atlantic crossing into the jet stream.
Formulas and scoring rules
- Duration
duration = arrival_UTC - departure_UTCEach local time is converted to UTC with its zone's offset on that date.- Arrival
arrival_local = departure_UTC + duration, shown in the arrival zone- Great-circle distance
Vincenty's inverse formula on the WGS 84 ellipsoidShown in km, statute miles (km / 1.609344) and nautical miles (km / 1.852).- Average speed
speed = distance / durationBlock time includes taxiing, so it is lower than cruising speed.
Limitations: what the result does not prove
- Time zones are not looked up from the airport - OurAirports does not publish them - so choose each zone yourself. A wrong zone gives a wrong duration.
- Schedules change. The tool calculates from the times you enter; it has no live flight data, delays or gate information.
- The distance is the shortest path over the ellipsoid. Real routes are longer because of airways, weather, restricted airspace and holding.
- A local time that does not exist (in a spring-forward gap) is moved forward; a local time that happens twice (in an autumn fall-back) uses the earlier instant. Both are flagged when they happen.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- IANA Time Zone Database
- OurAirports - open airport data (public domain)
- Vincenty (1975) - Direct and inverse solutions of geodesics on the ellipsoid, Survey Review
Frequently asked questions
Why does my flight arrive before it departs?
Because you are crossing time zones faster than the clock moves, or crossing the International Date Line eastbound. Auckland to Honolulu leaving at 19:00 lands at 06:00 the same calendar date after 9 hours in the air. The instants are in the right order; only the local clocks look backwards.
Does the flight time on my ticket include taxiing?
Yes. Airline schedules show block time, from pushing back at the gate to arriving at the gate, so it includes taxiing and often a buffer for congestion. Time in the air is usually 15 to 40 minutes shorter, depending on the airports.
How do daylight-saving changes affect flight duration?
They change the clock offset at one end, not the flight itself. If a zone springs forward during the night of your flight, the local arrival time looks an hour later than the duration suggests. Converting both ends to UTC, as this tool does, removes the confusion.
Why are eastbound and westbound flights different lengths?
Mostly winds. Jet streams in the mid-latitudes blow from west to east, so eastbound flights get a tailwind and westbound flights fight a headwind. London to New York is typically an hour or more longer than New York to London on the same aircraft.
What is the difference between great-circle distance and flight distance?
Great-circle distance is the shortest path between two points on the Earth's surface. Actual flight paths follow airways and weather routing, avoid closed airspace and include climb, descent and holding, so the distance flown is usually a few per cent longer.
Last reviewed by the A2Z.Tools team against the sources listed above.
