Time Difference Calculator (between two dates & times, any time zone)

Understanding the time difference calculator — concept and principle

This calculator finds the exact time between two moments, each with its own date, time and time zone. Use it for flight durations across time zones, international calls and meetings, shift lengths or countdowns.

How it is calculated

Each moment in UTC = local date and time − UTC offset

Difference = end (UTC) − start (UTC)

• The difference is shown in hours, in total minutes, in total days, and as whole days plus hours and minutes.
• Offsets are in hours east of UTC: Korea +9, London 0 in winter and +1 in summer, New York −5 in winter and −4 in summer. Half-hour offsets such as India's 5.5 work too.
• If the end is before the start, the result is negative and the page says so.

The principle

Local clock times are only comparable once they are put on one common clock. Coordinated Universal Time (UTC) is that clock. A time zone's offset says how far its clocks run ahead of UTC, so subtracting the offset converts local time to UTC: 22:10 in Seoul (UTC+9) is 13:10 UTC. Once both moments are in UTC, the gap is simple subtraction. ISO 8601 writes these offsets as +09:00 or +00:00 after the time.

Worked example

Default inputs: start today at 22:10, UTC+9; end tomorrow at 04:25, UTC+0.

1. Start in UTC = 22:10 − 9 h = 13:10 UTC today.
2. End in UTC = 04:25 − 0 h = 04:25 UTC tomorrow.
3. Difference = from 13:10 to 04:25 the next day = 15 h 15 min = 915 minutes.
4. In hours = 915 ÷ 60 = 15.25; whole days 0, plus 15 h 15 min.
5. In days = 915 ÷ 1,440 = 0.635, shown as 0.64; order: end is after start.

How to read the result

For a flight, the result is the true time in the air plus taxiing, even though the clocks may suggest something very different; this example looks like a gap of about 6 hours on the clocks but lasts over 15 hours. Check whether either place is on daylight saving time on the date you entered, because the offset changes by one hour in many countries in spring and autumn. Korea does not currently use daylight saving time.

Common mistakes

• Using the summer offset in winter, or the other way round.
• Adding the offset instead of subtracting it.
• Entering a 12-hour time without converting to 24-hour (10:10 pm is 22:10).
• Mixing up which date belongs to which moment.

Frequently asked questions

What is the time difference between Seoul and London?

9 hours in winter (UTC+9 vs UTC+0) and 8 hours when the UK is on summer time.

Does it work across the International Date Line?

Yes, as long as each local date and offset is entered correctly; converting both to UTC takes care of it.

Can I use it for two times in the same place?

Yes. Enter the same offset in both boxes.

Sources: ISO 8601-1:2019, Date and time — Representations for information interchange · IANA Time Zone Database (tz database)