World Clock

UTC (Coordinated Universal Time) is the primary time standard by which the world regulates clocks. GMT (Greenwich Mean Time) is essentially the same as UTC — both are at 0° longitude with no offset. The difference: GMT is a time zone used by some countries, while UTC is an atomic time standard. For practical purposes, UTC+0 and GMT are interchangeable.

Most countries use whole-hour offsets from UTC, but some chose unusual offsets for geographic or political reasons. India (UTC+5:30), Sri Lanka (UTC+5:30), Afghanistan (UTC+4:30), and Nepal (UTC+5:45) use non-standard offsets. Australia's Lord Howe Island uses UTC+10:30 in winter and UTC+11 in summer.

DST is the practice of advancing clocks by 1 hour during warmer months so evenings have more daylight. The US "springs forward" in March and "falls back" in November. Europe follows similar dates. Many countries do not observe DST, including China, Japan, India, and most of Africa and Asia. Our clocks reflect current DST status automatically.

The International Date Line (IDL) is an imaginary boundary at approximately 180° longitude in the Pacific Ocean. Crossing it westward advances the date by one day; crossing eastward moves it back. This is why Samoa and Tonga are almost a full day ahead of Hawaii despite being geographically close.