Timezone guides
Fact-checked, source-linked guides on how time works around the world.
Every guide is built on primary sources: the IANA timezone database, peer-reviewed chronobiology research, and the actual policies of the countries involved. No listicles. No recycled trivia. Just the real answers to questions people actually search for about time.
Fundamentals
Core concepts: what timezones are, how UTC and GMT differ, and why the date line zigzags.
Time Zones Explained: How the World Tells Time
From sundials to railroad schedules to the IANA database, the story of how humanity agreed on what time it is, and all the places it refused to agree.
UTC vs GMT: What's the Difference?
GMT is solar. UTC is atomic. They read the same on a clock but are built on entirely different foundations, and the distinction matters more than most people realize.
The International Date Line: Where Today Becomes Tomorrow
A line in the Pacific Ocean where the calendar changes, it zigzags around island nations for political reasons, and Jules Verne built a plot twist on it.
Practical
Scheduling meetings, converting military time, and working across timezones without losing your mind.
How to Schedule Meetings Across Time Zones
The practical guide to finding meeting times that work across timezones, with tools and strategies for remote teams.
Military Time: The 24-Hour Clock Explained
Why the military, aviation, and medicine abandoned AM and PM, and how the 24-hour clock removes an entire category of fatal ambiguity.
Science and Policy
The biology of jet lag and why most countries abandoned daylight saving.
Jet Lag: The Science of Crossing Time Zones
What happens to your body when you cross timezones, why eastbound is worse, and what the science says about recovery.
Countries That Don't Observe Daylight Saving Time
Most of the world's population never changes their clocks, and the reasons range from geography to imperial history to a national referendum that failed.
Tools
The guides above explain the theory. These tools do the maths for you.
- World Timezone Map with all 37 UTC offsets and country links
- Every Timezone, Right Now with live sun-brightness rendering
- All Cities with local time, sunrise, sunset, and DST status
Frequently Asked Questions
How many timezones are there?
There are 37 distinct UTC offsets in use worldwide, not the theoretical 24. Half-hour offsets (India, Iran) and quarter-hour offsets (Nepal) bring the total above the standard count.
What is the difference between UTC and GMT?
UTC is defined by atomic clocks and is the modern international standard. GMT is an older astronomical definition based on solar observations from Greenwich. They show the same time on a clock but are built on different foundations.
How do I schedule a meeting across timezones?
Find the business-hours overlap window between participants. For common routes like New York to London, the sweet spot is 9am to 11am US Eastern (2pm to 4pm London). Our scheduling guide covers every major corridor.
Why do some countries not observe daylight saving?
Countries near the equator have roughly equal day and night year-round, so clock changes offer no benefit. Others tried DST and abandoned it: Japan (1952), Russia (2014), Brazil (2019), Turkey (2016).
What is military time?
Military time uses the 24-hour clock format (0000 to 2359) to eliminate AM/PM ambiguity. It is standard in the military, aviation, medicine, and most countries outside the US.