To convert time between time zones, start from a known reference time, identify the time zone offset for each location, and account for daylight saving time if it applies. The most reliable method is to convert both times to Coordinated Universal Time (UTC) first, then convert to the destination time zone.

For example, if it is 3:00 PM in New York during standard time, it is 8:00 PM in London and 7:00 AM the next day in Sydney—depending on each location’s daylight saving rules.

Understand Time Zone Offsets

A time zone offset shows how far a location is from UTC.

• UTC+0: The local time is the same as UTC.
• UTC+5: Local time is 5 hours ahead of UTC.
• UTC-8: Local time is 8 hours behind UTC.

To convert from one time zone to another:

\text{Destination time} = \text{Original time} + (\text{Destination offset} - \text{Original offset})

Example

Convert 2:00 PM UTC to India Standard Time (IST), which is UTC+5:30.

2{:}00 \text{ PM} + 5{:}30 = 7{:}30 \text{ PM}

So, 2:00 PM UTC is 7:30 PM in India.

Use UTC as Your Reference

UTC is the best reference point because it does not observe daylight saving time. When scheduling across countries, convert both local times to UTC first.

Example: New York to Tokyo

Suppose it is 9:00 AM in New York during Eastern Standard Time (EST), which is UTC-5.

1. Convert New York time to UTC:
   9{:}00 \text{ AM} + 5 \text{ hours} = 2{:}00 \text{ PM UTC}
2. Convert UTC to Japan Standard Time (JST), which is UTC+9:
   2{:}00 \text{ PM} + 9 \text{ hours} = 11{:}00 \text{ PM}

So, 9:00 AM in New York is 11:00 PM the same day in Tokyo.

Account for Daylight Saving Time

Daylight saving time (DST) changes a location’s UTC offset for part of the year. Not every country uses it, and the start and end dates differ by country and region.

For example:

• New York uses Eastern Time: UTC-5 during standard time and UTC-4 during daylight saving time.
• London uses GMT: UTC+0 during standard time and BST: UTC+1 during daylight saving time.
• India uses IST year-round: UTC+5:30.
• Japan uses JST year-round: UTC+9.

A time that works in January may not work in July because one location may be observing DST while the other is not.

Example: London and New York

At 12:00 PM in London:

• During winter, New York is 5 hours behind: 7:00 AM
• During summer, New York may be 5 hours behind or 6 hours behind, depending on whether both locations are observing daylight saving time at that moment

This is why you should always check the date as well as the time. A meeting scheduled for “3:00 PM London time” can correspond to different New York times at different points in the year.

Convert Time Zones Step by Step

Use this process for any conversion:

1. Write down the original date and time.
2. Identify the original time zone and its UTC offset on that date.
3. Convert the original time to UTC.
4. Identify the destination time zone and its UTC offset on that date.
5. Convert UTC to the destination time.
6. Check whether the date changes.
7. Confirm daylight saving time for both locations.

Example: Los Angeles to Berlin

It is 6:00 AM in Los Angeles during Pacific Daylight Time (PDT), UTC-7. Berlin is on Central European Summer Time (CEST), UTC+2.

1. Convert Los Angeles to UTC:
   6{:}00 \text{ AM} + 7 \text{ hours} = 1{:}00 \text{ PM UTC}
2. Convert UTC to Berlin:
   1{:}00 \text{ PM} + 2 \text{ hours} = 3{:}00 \text{ PM}

So, 6:00 AM in Los Angeles is 3:00 PM in Berlin.

Handle Date Changes

Time zone conversion can move an event to the previous or next day.

Example: New York to Sydney

It is 8:00 PM on Friday in New York during EST, UTC-5. Sydney is on Australian Eastern Daylight Time, UTC+11.

1. Convert New York to UTC:
   8{:}00 \text{ PM} + 5 \text{ hours} = 1{:}00 \text{ AM Saturday UTC}
2. Convert UTC to Sydney:
   1{:}00 \text{ AM Saturday} + 11 \text{ hours} = 12{:}00 \text{ PM Saturday}

So, 8:00 PM Friday in New York is noon Saturday in Sydney.

Always include the date when scheduling international meetings. Saying “8:00 PM New York time” is incomplete if the recipient needs to know whether it falls on their Friday, Saturday, or Sunday.

Convert Time Zones on a Phone or Computer

Most devices can show multiple time zones automatically.

iPhone or iPad

1. Open the Clock app.
2. Tap World Clock.
3. Tap the plus button.
4. Add the cities you need.
5. Compare the current times side by side.

Android

1. Open the Clock app.
2. Tap Clock or World Clock.
3. Tap the plus button.
4. Add the cities or time zones you need.
5. View the local times for each location.

Windows or Mac

Search for “world clock” or add additional clocks in your operating system’s clock settings. You can usually display several time zones at once, which is helpful for remote teams and international clients.

Schedule International Meetings Clearly

Avoid confusion by using a single reference time and stating the date.

A clear meeting invitation might say:

Meeting: Tuesday, March 10
3:00 PM UTC
11:00 AM New York (EDT)
4:00 PM London (BST)
8:30 PM India (IST)

Best practices:

• Use a specific date, not just a weekday.
• State the time zone explicitly.
• Use UTC for global teams when possible.
• Include the recipient’s local time in the invitation.
• Avoid phrases like “tomorrow at 9” without specifying the time zone.
• Check DST changes before recurring meetings.

Common Time Zone Mistakes

Assuming daylight saving time applies everywhere

Many countries and regions do not observe DST. Others change on different dates. Always check the specific location and date.

Confusing GMT and UTC

GMT and UTC are often used interchangeably in everyday scheduling, but UTC is the modern international time standard. For technical systems and precise scheduling, use UTC.

Forgetting half-hour and 45-minute offsets

Not every time zone is a whole number of hours from UTC. Examples include India at UTC+5:30, Nepal at UTC+5:45, and parts of Australia at UTC+9:30.

Ignoring the date line

Crossing the International Date Line can change the date by a full day. A flight or meeting may arrive on the next calendar day even if the travel time is short.

Relying on memory for recurring meetings

DST changes can shift a recurring meeting by an hour in some locations. Review recurring events after daylight saving changes.

Quick Reference

Convert through UTC, check daylight saving time for the exact date, and always state the date alongside the time. For international meetings, include each participant’s local time to prevent missed calls and scheduling errors.