Your afternoon can be someone else’s morning
Imagine calling a friend far away. You have just finished lunch, but your friend is eating breakfast. Your clocks show different times.
Earth turns, so different places face the Sun at different moments. If every clock showed the same local time, “nine in the morning” could happen in darkness in some places.
A time zone is an area that follows the same rules for its clocks.
Why aren’t time zones straight stripes?
You might expect neat stripes around the globe. Real life is less tidy.
People often want towns in the same region or country to share a clock time. Governments choose the rules, so the boundaries bend around borders and places where people live.
Where a place sits on the globe helps explain its daylight. It does not, by itself, tell you the exact time on its clocks.
UTC is a shared starting clock
UTC is the common time reference used to compare clocks around the world. Think of it as our starting clock.
UTC+2 means a local clock is two hours ahead of that starting clock. When UTC shows 12 noon, the local clock shows 2 in the afternoon.
UTC−3 means three hours behind. When UTC shows 12 noon, that local clock shows 9 in the morning.
That difference is called an offset. The plus sign means ahead; the minus sign means behind.
Follow one call, step by step
For this made-up example, City A uses UTC+2 and City B uses UTC−3. It is 2 in the afternoon in City A, also written as 14:00.
- Find the starting clock. City A is two hours ahead of UTC. Go back two hours: from 2 in the afternoon to 12 noon.
- Find City B. Its clock is three hours behind UTC. Go back from noon to 11, then 10, then 9.
- It is 9 in the morning in City B. That is written as 09:00.
Three clocks at the same moment
| Clock | Time |
|---|---|
| City A: two hours ahead of UTC | 2 in the afternoon (14:00) |
| UTC: our starting clock | 12 noon (12:00) |
| City B: three hours behind UTC | 9 in the morning (09:00) |
For a real call, check the city and date
Some places move their clocks forward or back during the year. Others do not. This is often called daylight saving time.
So a place can use a different offset at different times of year. A time zone includes those rules, not just today’s difference from UTC.
For a real call or journey, use a calendar or world-clock tool with both the city and the date. IANA keeps a database of these clock rules as they change.