Timezones are surprisingly complex, with daylight saving time, political changes, and historical variations. IP-based timezone detection offers a simple way to show users times in their local context.
IANA Timezone Database
The IANA (Internet Assigned Numbers Authority) timezone database is the standard for timezone data. Timezones are identified by strings like "America/New_York" or "Europe/London". These identifiers handle daylight saving time automatically. Avoid using abbreviations like "EST" or "PST"—they're ambiguous and don't account for DST.
Detecting User Timezone
Three methods exist: IP-based detection (fast, works without permissions, ~85% accurate), browser JavaScript (Intl.DateTimeFormat().resolvedOptions().timeZone returns client timezone), and explicit user selection (most accurate but requires user action). Combine methods for best results: use IP detection as default, allow user override.
Storing and Converting Times
Always store timestamps in UTC in your database. Convert to user's local timezone only for display. Include timezone information when communicating times to users. For scheduled events, store the event timezone separately (a meeting at "2pm EST" stays at 2pm EST even when DST changes).