What Is UTC and Why It Matters
2026-02-06 · 8 min read
UTC means Coordinated Universal Time. The abbreviation was chosen as a language-neutral compromise between the English and French word orders (CUT and TUC).
What UTC Is Based On
UTC is based on atomic clocks, not solar time. The BIPM in Paris coordinates UTC using data from roughly 400 atomic clocks operated by national timing labs worldwide.
UTC vs GMT
GMT began as a mean solar-time reference tied to Greenwich. UTC replaced GMT in precision timing during the 1960s; GMT remains a timezone label, while UTC is the global time standard.
Leap Seconds
Leap seconds keep UTC within 0.9 seconds of Earth rotation (UT1). The last leap second was added in December 2016, and international standards bodies agreed to retire leap seconds by 2035.
Why UTC Matters
UTC anchors aviation schedules, military operations, scientific data, cloud logs, and international business systems. Using UTC timestamps avoids ambiguity during DST transitions.
Offset Examples
- UTC+0: London in GMT period
- UTC-5: New York in EST period
- UTC+9: Tokyo (JST year-round)