Understanding timezones
The world is divided into 24 primary timezone zones, each roughly 15 degrees of longitude wide. When it's noon in London (UTC+0), it's 7am in New York (UTC−5) and 7pm in Tokyo (UTC+9).
UTC — the global reference point
UTC (Coordinated Universal Time) is the universal time standard. All other timezones are expressed as offsets from UTC:
- New York: UTC−5 (EST) or UTC−4 (EDT during daylight saving)
- London: UTC+0 (GMT) or UTC+1 (BST during summer)
- Ho Chi Minh City: UTC+7 (no daylight saving)
- Tokyo: UTC+9 (no daylight saving)
Daylight Saving Time (DST)
Many countries shift their clocks forward by 1 hour in summer to extend evening daylight. This means timezone offsets change twice a year.
Countries that observe DST: USA, Canada, most of Europe, Australia (opposite seasons)
Countries that do NOT observe DST: Vietnam, Japan, China, India, most of Southeast Asia, most of Africa
This is why "New York is always 12 hours behind Tokyo" is wrong — it's 14 hours behind in winter and 13 hours behind during US daylight saving time.
Common timezone abbreviations
| Abbreviation | Full name | UTC offset |
|---|---|---|
| UTC | Coordinated Universal Time | UTC+0 |
| EST | Eastern Standard Time | UTC−5 |
| EDT | Eastern Daylight Time | UTC−4 |
| PST | Pacific Standard Time | UTC−8 |
| PDT | Pacific Daylight Time | UTC−7 |
| GMT | Greenwich Mean Time | UTC+0 |
| BST | British Summer Time | UTC+1 |
| CET | Central European Time | UTC+1 |
| IST | India Standard Time | UTC+5:30 |
| ICT | Indochina Time (Vietnam) | UTC+7 |
| CST | China Standard Time | UTC+8 |
| JST | Japan Standard Time | UTC+9 |
| AEST | Australian Eastern Standard | UTC+10 |
Best practices for scheduling international meetings
Working across timezones is challenging. The key is finding overlap in business hours (9am–6pm) across all participants' timezones.
For a team spread across New York, London, and Ho Chi Minh City:
- New York business hours: 9am–6pm EST = 2pm–11pm GMT = 9pm–6am ICT
- London business hours: 9am–6pm GMT = 4am–1pm EST = 4pm–1am ICT
- Ho Chi Minh business hours: 9am–6pm ICT = 2am–11am GMT = 9pm–6am EST
The only overlap in business hours is 2pm–6pm London time (9am–1pm New York, 8pm–midnight Vietnam). Someone will always be working outside normal hours.
How to convert timezones free
- Go to Timezone Converter
- Enter the time you want to convert
- Select source and destination timezones
- View all timezones simultaneously in one table
- Use meeting planner mode to find business hour overlaps