World Clock - Time Zone Converter & Meeting Planner

UTC (Coordinated Universal Time) is the primary time standard used globally, based on atomic clocks. GMT (Greenwich Mean Time) is a timezone (UTC+0) tied to solar time at Greenwich, UK. While often used interchangeably, UTC is more precise. All timezones express offset from UTC (e.g., EST is UTC-5, JST is UTC+9). Always store timestamps in UTC and convert to local time for display.

Store all timestamps in UTC in databases and logs. Use timezone-aware libraries (moment-timezone, date-fns-tz, Python pytz, Java ZonedDateTime) instead of manual offsets. Never store local times without timezone context. Account for DST transitions. Use IANA timezone identifiers (America/New_York) not abbreviations (EST) which are ambiguous. Test edge cases: DST transitions, leap seconds, historical timezone changes.

DST shifts clocks forward (spring) and backward (fall) to extend evening daylight. Not all countries observe DST; those that do change on different dates. This creates scheduling complexity: a weekly meeting at "10 AM EST" will shift relative to regions without DST. Solutions: schedule in UTC, use recurring meeting tools that handle DST, or specify "floating" times that adjust with local clocks.

Identify all participants' timezones, find overlapping business hours (typically 9 AM-6 PM local). Tools like World Time Buddy help visualize overlaps. Be fair—rotate meeting times if one region always accommodates. Document meetings in UTC and local times. Send calendar invites with timezone data (ICS format handles this). Consider asynchronous collaboration for extreme time differences, reducing synchronous meeting burden.

Assuming everyone follows your DST schedule, using ambiguous abbreviations (CST could mean Central Standard Time or China Standard Time), forgetting some regions have 30/45-minute offsets (India UTC+5:30, Nepal UTC+5:45), not testing DST transition periods, hardcoding timezone logic instead of using libraries, and displaying times without timezone context. Always clarify timezone and consider using 24-hour format for clarity.

Timezones change: countries adjust offsets, DST rules evolve, regions rename zones. The IANA Time Zone Database tracks these changes. When displaying historical data, use the timezone rules that were active at that time. Modern libraries with updated IANA data handle this automatically. Regularly update timezone databases in applications—outdated data causes incorrect historical and future time conversions.

Use ISO 8601 format (2025-01-30T14:30:00Z for UTC, 2025-01-30T14:30:00-05:00 for local with offset). Always include timezone information. Consider 24-hour format to avoid AM/PM confusion. Display both local time and UTC for clarity in global contexts. In user interfaces, detect user timezone automatically but allow override. For scheduling, show times in recipient's timezone: "3 PM your time (9 PM UTC)".