Scheduling a call with colleagues in Tokyo, London, and New York? Time zones can make simple coordination feel like solving a puzzle. Understanding how they work helps you navigate our globally connected world.
Why Time Zones Exist
Before standardized time, every town set clocks to local solar noon. This worked fine until railroads connected distant places. Trains couldn't run on schedules when every station had different time.
In 1883, US railroads established four time zones. The following year, the International Meridian Conference divided the world into 24 zones, each representing one hour.
Check times anywhere with our world clock.
How Time Zones Work
The Earth rotates 360 degrees in 24 hours—15 degrees per hour. Each time zone theoretically covers 15 degrees of longitude, though political boundaries create irregular shapes.
UTC: The Reference Point
Coordinated Universal Time (UTC) is the global standard. Time zones are expressed as offsets from UTC:
- New York: UTC-5 (or UTC-4 during Daylight Saving)
- London: UTC+0 (or UTC+1 during summer)
- Tokyo: UTC+9 (no daylight saving)
The International Date Line
Running through the Pacific Ocean, this line marks where the calendar date changes. Cross westward and add a day; cross eastward and subtract one.
Daylight Saving Time
Many regions adjust clocks forward in spring ("spring forward") and back in fall ("fall back"). This complicates international scheduling:
- Not all countries observe DST
- Start and end dates vary by country
- Southern Hemisphere is opposite (summer in December)
- Some regions within countries don't observe it
Countries like Japan, China, and India don't use DST. Arizona (except Navajo Nation) stays on standard time year-round.
Unusual Time Zones
Half-Hour Offsets
Some regions use 30-minute offsets:
- India: UTC+5:30
- Iran: UTC+3:30
- Newfoundland: UTC-3:30
Quarter-Hour Offsets
Nepal is UTC+5:45, and the Chatham Islands are UTC+12:45.
Countries Spanning Multiple Zones
- Russia: 11 time zones
- United States: 6 time zones (including Alaska and Hawaii)
- France: 12 time zones (including overseas territories)
Single Zone Despite Size
China uses only UTC+8, despite spanning what should be five zones. Noon in Beijing means sunrise in the far west.
Tips for Global Scheduling
Find Overlapping Hours
When teams span many zones, find the sweet spot where all can meet during working hours (even if some are early or late).
Rotate Meeting Times
Don't make the same region always take inconvenient times. Share the burden of off-hours meetings.
Use UTC for Documentation
Deadlines and timestamps in UTC avoid confusion about "which 5 PM?"
Add Time Zones to Invitations
Always include the time zone when scheduling. "3 PM EST" is clearer than "3 PM."
Convert Carefully Around DST
Double-check when scheduling near daylight saving transitions. A 9 AM meeting might shift for one party but not another.
Common Time Zone Pairs
Frequently needed conversions:
US East Coast to Europe
- New York to London: +5 hours
- New York to Paris: +6 hours
- New York to Berlin: +6 hours
US West Coast to Asia
- Los Angeles to Tokyo: +17 hours (next day)
- Los Angeles to Sydney: +19 hours (next day)
- Los Angeles to Singapore: +16 hours
Europe to Asia
- London to Dubai: +4 hours
- London to Singapore: +8 hours
- London to Sydney: +10/11 hours
Tools for Time Management
- World Clock - See times across cities
- Timestamp Converter - Convert Unix timestamps
- Date Calculator - Calculate date differences
Time Zone Best Practices for Teams
- Document team zones: Keep a shared reference of everyone's time zone
- Use calendar features: Modern calendars display events in each viewer's local time
- Enable world clocks: Add key cities to your phone's world clock
- Consider asynchronous work: Not everything needs real-time meetings
- Record meetings: Allows those in impossible time zones to catch up
Our world clock displays times in 50+ cities, making global coordination simple.
