Time Zone Converter

UTC (Coordinated Universal Time) is the primary time standard by which the world regulates clocks and time. GMT (Greenwich Mean Time) is a time zone that has no offset from UTC. For most practical purposes they are equivalent, but UTC is the modern standard used in computing and networking. GMT is a geographical time zone while UTC is an atomic time standard. In code, always prefer UTC.

Daylight Saving Time (DST) is the practice of advancing clocks during warmer months so that evening daylight lasts longer. Most of the US springs forward 1 hour in March and falls back in November. The EU shifts in March and October. Not all regions observe DST — Arizona (US), China, Japan, and most of Africa and Southeast Asia do not. DST transitions are a common source of bugs in scheduling software.

ISO 8601 is the international standard for date and time representation. Example: 2024-03-15T14:30:00Z (UTC) or 2024-03-15T10:30:00-04:00 (with offset). The Z suffix means UTC. Offsets like -04:00 indicate hours behind UTC. Always include timezone info in API timestamps — never send "naked" datetimes without a zone, as they are ambiguous and cause off-by-hour bugs.

Use the Intl.DateTimeFormat API: new Intl.DateTimeFormat('en-US', { timeZone: 'America/New_York', hour: '2-digit', minute: '2-digit' }).format(new Date()). Or use toLocaleString: new Date().toLocaleString('en-US', { timeZone: 'Europe/Paris' }). For full timezone-aware date math, use a library like date-fns-tz or Temporal (the modern JS Temporal API). Avoid storing times as plain strings without timezone info.

IANA time zone names are the standard identifiers used in software, such as America/New_York, Europe/London, Asia/Tokyo, Australia/Sydney. They follow the format Region/City. These names are preferred over abbreviations like EST or PST because abbreviations are ambiguous (CST means different things in different regions). JavaScript's Intl API and most server-side frameworks use IANA names.