What Is a World Clock?
A world clock displays the current local time simultaneously in multiple cities around the globe. It is an essential tool for business professionals who collaborate across continents, travellers planning trips, remote teams scheduling meetings, and anyone who needs to track what time it is somewhere else in the world right now.
Unlike a time zone converter (which converts a specific datetime), a world clock continuously displays live time — updating every second — so you always see the current moment in each city.
How This World Clock Works
This clock uses the browser's Intl.DateTimeFormat API with IANA time zone identifiers to render each city's local time. A setInterval runs every second to refresh all 15 city cards. Day/night status is determined by whether the local hour is between 6 AM and 8 PM — night cards are shown with a dark background for quick visual scanning.
Cities Covered
The world clock shows all major global hubs: New York, Los Angeles, São Paulo (Americas) · London, Paris, Berlin, Moscow (Europe) · Cairo, Johannesburg, Dubai (Africa / Middle East) · Mumbai, Bangkok, Singapore, Shanghai, Tokyo, Sydney, Auckland (Asia-Pacific). These cities collectively represent most of the world's major time zones.
Understanding UTC Offsets
Each card shows the UTC offset — how many hours ahead or behind Coordinated Universal Time (UTC) that city currently is. The offset can change for cities that observe daylight saving time: New York moves from UTC−5 to UTC−4 in summer, while Tokyo stays at UTC+9 year-round. This clock uses IANA time zone data which automatically handles these transitions.
Frequently Asked Questions
How do I know if it is day or night in another city?
Cards with a dark background indicate nighttime (local hour before 6 AM or after 8 PM). Cards with a white background indicate daytime. This visual distinction lets you quickly see which cities are currently active or asleep.
How often does the world clock update?
Every second, using setInterval. Times are generated fresh using Intl.DateTimeFormat with each city's IANA time zone identifier, so daylight saving transitions are automatically applied.
Which cities are included?
New York, Los Angeles, London, Paris, Berlin, Moscow, Dubai, Mumbai, Bangkok, Singapore, Tokyo, Sydney, Auckland, São Paulo, and Cairo — covering all major continents and representing most global time zones.
What is UTC?
UTC (Coordinated Universal Time) is the global time reference with zero offset. All time zones are expressed as UTC+X or UTC−X. UTC is based on atomic clocks and never observes daylight saving time, making it a stable absolute reference.
Why do some cities have the same UTC offset?
Adjacent cities in the same region often share an offset. However, political decisions override geography — China uses UTC+8 for the entire country despite its geographic width spanning 5 natural time zones. Singapore and Shanghai are both UTC+8 for similar political reasons.