Guides
Plain explanations of how time zones, UTC and daylight saving time work.
What is a time zone?
What a time zone is, why the world uses them, and how they're named.
How time zones work
How offsets, boundaries and local rules decide the time in a place.
UTC vs GMT
How UTC and GMT differ, and when the difference matters.
Daylight saving time
What daylight saving time is, who uses it, and when clocks change.
How to convert time zones
How to work out the time in another time zone.
Scheduling across time zones
How to find a meeting time that works in several cities.
Traveling across time zones
Keeping track of time when you travel between time zones.
Programming with time zones
How to store, convert and display times correctly in software.
Time zones and stock markets
How time zones shape stock market opening hours around the world.
Time zones for pilots
How pilots and air traffic control handle time zones.