Time zone conversion:
convert IST to London, Dubai and New York

How do you convert between time zones?

Go through UTC every time. Subtract the offset of the place you are starting from to reach UTC, then add the offset of the place you want. This works for any pair of zones, including those with 30- or 45-minute offsets.

India uses a single zone, Indian Standard Time, which is UTC+5:30. India does not use daylight saving, so the offset is the same all year. That is why the gap between India and places that do change their clocks varies during the year, while India's own offset never moves.

Going through UTC means you only need to know one number for each city. Converting directly between every pair of places would need a separate rule for each pair, and the rules change when daylight saving does.

A place's offset is how far its clocks are ahead of UTC (plus) or behind it (minus). Dubai is UTC+4, Singapore is UTC+8 and New York is UTC−5 in winter and UTC−4 in summer.

Time zone conversion formula

1. 1Write the start time on a 24-hour clock.
2. 2Subtract the starting zone's offset to get UTC.
3. 3Add the destination zone's offset.
4. 4If the answer is below 00:00 or above 24:00, adjust the date by one day.

Try one the other way round. A call at 3:30 PM in Tokyo (UTC+9) is 15:30 − 9:00 = 06:30 UTC, and adding 5:30 gives 12:00 noon in India.

A second case: 8:30 PM IST is 20:30 − 5:30 = 15:00 UTC. New York in daylight time (UTC−4) is 11:00 AM, and in standard time (UTC−5) it is 10:00 AM.

Work in minutes if the offsets have halves. India's 5:30 is 330 minutes, so the hour to minute converter on this page turns 5.5 hours into 330 minutes in one step.

Worked example: a 10:00 AM IST meeting

A team in Bengaluru schedules a call for 10:00 IST and needs the time in London, Dubai and New York in the summer.

The 10:00 IST slot works for Dubai, but it is the middle of the night in New York. A slot such as 18:30 IST is 14:00 in London, 17:00 in Dubai and 09:00 in New York, so it falls inside normal working hours in all three.

What 9:00 AM IST becomes elsewhere

Read the last column as the clock time you would see at that place at the same moment as 9:00 AM in India. A note of 'previous day' means the date there is one day earlier.

Southern-hemisphere places add a twist. Sydney is UTC+10 in its winter and UTC+11 in its summer, so its lead over India is 4:30 for part of the year and 5:30 for the rest.

Nepal is the neat edge case. Its offset is UTC+5:45, so it is 15 minutes ahead of India, and 9:00 AM IST is 9:15 AM in Kathmandu.

Offsets in this table are typical values. Daylight saving changes them for part of the year, and the dates differ from country to country, so confirm the date you are converting.

When the date changes

Going west means clocks are behind, and the date can step back. 02:00 on the 15th in India is 20:30 UTC on the 14th, and in New York (UTC−4) it is 16:30 on the 14th.

Going east, the opposite can happen. A 23:30 IST call is 02:00 the next day in Singapore, which is 2½ hours ahead. Always write the date next to the time when you share a meeting across a day boundary.

Working hours show why the gap matters. Assume India works 9:30 to 18:30 and the UK works 9:00 to 17:00. When London is on summer time, the UK day runs from 13:30 to 21:30 IST, so the overlap is 13:30 to 18:30, five hours. In winter, UK hours run 14:30 to 22:30 IST and the overlap shrinks to four hours.

Flights and arrival times

A flight departure and arrival are both in local time, so the duration is not simply arrival minus departure. Use the formula: local arrival = local departure + flight duration + (destination offset − origin offset).

Take a Delhi to Singapore flight leaving at 23:30 IST. Assume a flight time of 5 h 30 min. Singapore is 2 h 30 min ahead of India, so arrival is 23:30 + 5:30 + 2:30 = 31:30, which is 07:30 the next day.

You can also reverse it to find a flight's length. Suppose a flight leaves Delhi at 02:10 IST and lands in Dubai at 04:10 local time. Dubai is 1 h 30 min behind India, so the duration is (04:10 − 02:10) + 1:30 = 3 h 30 min.

If you do not know the flight time, the trip time calculator on this page estimates it from distance and speed. Convert the answer to minutes first, then add the offset difference.

Mistakes with time zone conversion

• Using ambiguous abbreviations. IST can mean India, Ireland or Israel, and CST can mean US Central, China or Cuba. Say UTC offsets or city names.
• Forgetting daylight saving. New York is UTC−5 in winter and UTC−4 in summer, so the gap from India shifts by an hour.
• Mixing up 12:00 AM and 12:00 PM. Use 24-hour time when you send a schedule.
• Applying the offset in the wrong direction. If the destination is ahead of UTC, you add its offset, not subtract.
• Assuming every zone has a whole-hour offset. India is +5:30 and Nepal is +5:45.
• Assuming the gap with another country is constant. The UK and the US change their clocks on different dates, so for a few weeks the gap between them can differ by an hour.

Before you send an invite, write the time in both zones with the date, for example '18:30 IST / 14:00 London on 12 Oct'. It costs a few seconds and prevents most scheduling errors.