What is UTC?
Coordinated Universal Time — the world's time standard
UTC, short for Coordinated Universal Time, is the primary time standard by which the world regulates clocks and time. It is the basis for civil time internationally and the reference point from which all time zones are calculated.
From GMT to UTC
Before UTC, the world used Greenwich Mean Time (GMT) — solar time at the Royal Observatory in Greenwich, London. GMT became the global standard in 1884 when the International Meridian Conference designated the Greenwich meridian as the prime meridian (0° longitude).
In 1960, atomic clocks became precise enough to replace astronomical observations for timekeeping. In 1972, the international community adopted UTC, which is based on International Atomic Time (TAI) — maintained by a network of over 400 atomic clocks around the world — but adjusted with occasional leap seconds to stay within 0.9 seconds of Earth's actual rotation.
UTC vs GMT — What's the Difference?
In everyday use, UTC and GMT refer to the same offset: both represent time at 0° longitude, with no daylight saving adjustment. However, they are technically different:
- GMT is an astronomical standard based on Earth's rotation — it varies slightly as the planet's rotation speed changes.
- UTC is derived from atomic clocks and is perfectly uniform. It is kept in sync with Earth's rotation via leap seconds.
For all practical purposes — scheduling, computing, aviation — UTC is used. GMT is sometimes still seen in legal and broadcast contexts in the UK.
How UTC Offsets Work
Every time zone in the world is defined as an offset from UTC, written as UTC+H or UTC−H, where H is the number of hours ahead or behind UTC.
| Offset | Example locations |
|---|---|
| UTC−12:00 | Baker Island, Howland Island (uninhabited) |
| UTC−8:00 | Los Angeles, Seattle, Vancouver |
| UTC−5:00 | New York, Toronto, Bogotá |
| UTC+0:00 | London (winter), Reykjavik, Accra |
| UTC+1:00 | Paris, Berlin, Lagos (winter offset) |
| UTC+3:00 | Moscow, Nairobi, Istanbul |
| UTC+5:30 | India (New Delhi, Mumbai) |
| UTC+8:00 | Beijing, Singapore, Perth |
| UTC+9:00 | Tokyo, Seoul |
| UTC+14:00 | Kiritimati (Line Islands) |
Note that not all offsets are full hours. India uses UTC+5:30, Nepal UTC+5:45, Iran UTC+3:30, and Australia's Lord Howe Island UTC+10:30. These half- and quarter-hour offsets exist for geographic or political reasons.
UTC and Daylight Saving Time
UTC itself never changes — it has no daylight saving adjustments. When a country observes daylight saving time, the local clocks shift by one hour, which simply changes the UTC offset. For example, London is at UTC+0 in winter and UTC+1 in summer. UTC remains constant; only the local offset changes.
Why UTC Matters
UTC is the backbone of modern global infrastructure:
- Aviation: All flight schedules, air traffic control, and weather reports use UTC (often called "Zulu time" in aviation).
- Internet: Servers log events and synchronize via UTC using the Network Time Protocol (NTP). The Unix timestamp — the number of seconds since January 1, 1970 — counts in UTC.
- Finance: Stock exchanges and international transactions are timestamped in UTC to ensure unambiguous ordering across time zones.
- GPS: GPS satellites broadcast time in UTC (technically GPS time, which differs from UTC by a fixed number of leap seconds).
- Space: NASA and other agencies use UTC for mission planning and communication windows.
The Current UTC Time
You can always see the exact current UTC time on our main page — click any timezone button and select UTC, or use the timezone map to explore how UTC offsets are distributed around the globe.