Convert time across global time zones and understand UTC, GMT, and daylight saving time.
Convert time instantly between any time zones worldwide.
Key concepts for working with time across the globe.
The primary time standard by which the world regulates clocks and time. Not affected by daylight saving time. Based on atomic clocks.
Time at the Royal Observatory in Greenwich, London. Historically the reference point for time zones. Often used interchangeably with UTC (though technically different).
Practice of advancing clocks during warmer months to extend evening daylight. Not all countries or regions observe DST, causing seasonal time offset changes.
Difference between a timezone and UTC, expressed as +/- hours and minutes. Can range from UTC-12 to UTC+14. Some timezones use 30 or 45-minute offsets.
The standard time zone database used by most software. Uses format "Continent/City" (e.g., America/New_York, Europe/London).
International standard for representing dates and times with timezone information. Unambiguous and machine-readable format.
Common time zones and their UTC offsets.
HST: UTC-10 (Hawaii)
PST: UTC-8 (Pacific)
MST: UTC-7 (Mountain)
CST: UTC-6 (Central)
EST: UTC-5 (Eastern)
AST: UTC-4 (Atlantic)
BRT: UTC-3 (Brazil)
GMT: UTC+0 (Greenwich)
CET: UTC+1 (Central Europe)
EET: UTC+2 (Eastern Europe)
MSK: UTC+3 (Moscow)
CAT: UTC+2 (Central Africa)
EAT: UTC+3 (East Africa)
GST: UTC+4 (Gulf)
IST: UTC+5:30 (India)
ICT: UTC+7 (Indochina)
CST: UTC+8 (China)
JST: UTC+9 (Japan)
KST: UTC+9 (Korea)
AEST: UTC+10 (East Australia)
ACST: UTC+9:30 (Central Australia)
NZST: UTC+12 (New Zealand)
FJT: UTC+12 (Fiji)
TOT: UTC+13 (Tonga)
Guidelines for handling time zones in software development.
Store all timestamps in UTC in your database. Convert to local time zones only for display. This prevents ambiguity and makes calculations consistent across time zones.
Use full IANA identifiers (e.g., "America/New_York") instead of abbreviations (e.g., "EST"). Abbreviations are ambiguous and don't account for DST changes.
Always use established libraries (Luxon, date-fns-tz, moment-timezone, etc.). Time zone rules change frequently, and libraries are kept up to date with the IANA database.
When scheduling future events, be aware that DST transitions can cause times to shift. Store the timezone along with the time, not just the offset.
Test your application with different time zones and DST scenarios. Edge cases often occur around DST transitions and when users are in different time zones.
Always show the time zone when displaying times to users. Use formats like "3:00 PM EST" or "15:00 UTC" to avoid confusion.