Are Flight Times in Local Time? Calculating Flight Duration and Why the Arrival Date Shifts
“Departs at 17:00, arrives at 10:00 the same morning.” Seeing this on an international booking screen is momentarily confusing. Every time on a ticket is in local time, so simply subtracting one from the other doesn’t give you the flight time. This article covers how to work out the duration, why dates jump backward or forward, and the booking situations where mistakes are most common.
Every time on the ticket is local time
The departure and arrival times on a ticket or booking confirmation are, without exception, the local times where each airport is. The departure time follows the clock at the origin, and the arrival time the clock at the destination. They aren’t converted to one common time zone, so subtracting one from the other doesn’t give you the flight time.
The same applies to airport departure boards, connection details and delay notices. A notice from an overseas airline saying “departure is delayed by 2 hours” is also based on a time written in local time.
The formula for flight duration
Take the difference in local times and add back the time difference, and you get the flight time. As a formula:
- Duration = (local arrival time − local departure time) + (origin’s UTC offset − destination’s UTC offset)
- If you arrive the next day or later, add 24 hours (48 hours for two days later) to the local arrival time before calculating.
Example 1: A flight leaving Tokyo (Haneda) at 17:00 and arriving in Los Angeles at 10:30 the same day. Tokyo is UTC+9, and Los Angeles is UTC−7 during daylight saving time. (10:30 − 17:00) = −6 hours 30 minutes, and (+9 − (−7)) = +16 hours. Add them and the flight time is 9 hours 30 minutes. The clock may have gone back to the morning, but you’ve actually flown for nearly 10 hours.
Example 2: The reverse direction, leaving Los Angeles at 12:00 and arriving at Haneda at 16:00 the next day. (16:00 + 24 hours − 12:00) = 28 hours, and (−7 − (+9)) = −16 hours. The result is 12 hours. The same route takes different times each way because the westerly jet stream makes eastbound flights faster.
If there’s no time difference, no calculation is needed. Japan and South Korea are both UTC+9, so departing at 10:00 and arriving at 12:30 is simply 2 hours 30 minutes. Start by checking whether there’s a time difference at all.
Flights where the date goes back, and where it goes forward
Seen from Japan, whether you fly east or west changes how the arrival date moves. Remember it by direction and booking screens will stop surprising you.
| Route | How the arrival date moves | How it looks |
|---|---|---|
| Japan → North America (eastbound) | Often the same date, with the clock going back | Departs in the evening, arrives the same morning |
| North America → Japan (westbound) | Goes forward a day | Departs at midday, arrives the next evening |
| Japan → Europe (westbound) | Often arrives the same day | Departs in the morning, arrives that evening. You fly about 12 hours but the clock moves only a few |
| Europe → Japan (eastbound) | Goes forward a day | Departs at night, arrives the next afternoon |
| Japan → Southeast Asia or Australia | Same date; small time difference | Reads the way you’d expect |
Flights to North America seem to go back in time because crossing the International Date Line in the Pacific eastbound moves the date back a day. Time doesn’t shrink in flight; the reference for the clock simply switches. Flights back to Japan cross the date line westbound, so the date moves forward a day.
Five booking situations where mistakes are common
- 1
Dates on flights just after midnight
“Departs 5 January, 00:20” is a flight you go to the airport for on the night of 4 January. Go by the date alone and head there during the day on the 5th, and you’re a full day late. When you book a red-eye, add the day you need to be at the airport to your calendar separately.
- 2
AM and PM in 12-hour notation
12:00 AM is midnight and 12:00 PM is noon. This trips many people up, so if in doubt, switch to 24-hour time to check.
- 3
Calculating connection times
Connection times are the difference between two local times at the same place, so you can subtract directly. But when connecting from an international to a domestic flight, there’s immigration, baggage claim and another security check. Even if it shows an hour and a half, the time you actually have to move is much shorter.
- 4
Linking separately booked tickets
If flights weren’t issued on one booking, the second won’t wait if the first is delayed. Leave a margin of a day, or book them together.
- 5
Dates for hotels, transfers and rental cars
The first night of your stay is the local date you arrive. On a flight arriving late at night, you won’t get into your room unless you book from the previous night. Airport transfers and rental car pick-up times are all specified in local time too.
The same logic applies to the start dates of travel insurance and eSIMs. Set them to start on the day you arrive rather than the day you leave, and your time in transit isn’t covered. For journeys that cross dates, it’s safer to start a day early.
Checking times before you fly
- 1
Check the current time at your destination and the difference
Use the World Time Zones tool to see the current time at your destination and its difference from Japan. Current times and differences for major countries are listed together, so you can see what time it is right now. During daylight saving periods, times are shown with it applied.
- 2
Note whether you arrive in the local morning or night
If you arrive late at night, you can’t plan anything that day. Also check now whether transport from the airport will be running at that time.
- 3
Calculate the duration and plan your time on board
Work out the flight time with the formula above and decide which part of the flight to sleep through. Sleeping during the destination’s night makes the adjustment after you land smaller.
- 4
Give family or work at home both times
Share both, such as “arrives 16:00 local time (9:00 next day, Japan time)”. Give only one and you may get calls at hours when you can’t answer.
FAQ
- Is the arrival time on a ticket in Japan time or local time?
- It’s the local time at the destination. The departure time is local time at the origin, so the two use different references. That’s why subtracting one from the other doesn’t give the flight time. To know it in Japan time, convert the local arrival time by adding or subtracting the difference from Japan.
- How do I calculate flight time?
- Take (local arrival time − local departure time) and add (origin’s UTC offset − destination’s UTC offset). If you arrive the next day, add 24 hours to the arrival time before calculating. For example, departing Tokyo at 17:00 and arriving in Los Angeles at 10:30 the same day gives −6 hours 30 minutes plus 16 hours, which is 9 hours 30 minutes.
- Why does my flight to the US arrive at an earlier time than it departs?
- Because crossing the International Date Line in the Pacific eastbound moves the date back a day, and local time there is behind Japan’s. On the clock you arrive before you left, but you’ve actually flown for around 10 hours. On the way back the date moves forward a day, so you effectively spend a day on the plane.
- When should I go to the airport for a flight just after midnight?
- On the night before the date printed on the ticket. For “departs on the 5th at 00:20”, head to the airport on the night of the 4th. When you book a red-eye, adding the date and time you need to be at the airport to your calendar separately prevents mix-ups. Also check whether your first hotel night needs to start the night before.
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