This page prints what your browser and operating system believe your timezone is: IANA identifier when exposed, offset from UTC, whether daylight saving is active, and local wall time. I once joined a Berlin stand-up while my laptop still reported Asia/Karachi after a redeye; Calendar sent the invite in UTC, Slack showed local strings in two zones, and only this style of check caught the OS toggle I had skipped during airport Wi‑Fi login. Below: how Intl resolves identifiers, why half-hour offsets exist, and where server-side IP guesses disagree with your clock.
UTC, GMT, and why IANA names beat three-letter abbreviations
UTC is the atomic-time-based civil standard the internet uses internally. GMT is a historical civil name; for scheduling web apps they are usually interchangeable at minute precision. Real-world rules live in the IANA Time Zone Database (often called tzdb or Olson database): identifiers like Asia/Karachi encode not only a fixed offset but the entire history of DST and government decrees for that region.
Abbreviations like PST or PKT are ambiguous (Pakistan no longer moves clocks for DST, but other countries reuse similar letters). Always store instants in UTC (see RFC 3339) and convert with an explicit zone id when rendering.
How this page reads your timezone
We call Intl.DateTimeFormat().resolvedOptions() in the browser. That returns timeZone when the engine exposes it (Chromium, Firefox, Safari on current releases), plus locale and calendar preferences. A server-rendered guess from your IP alone can disagree: VPN users often show a European IP while the laptop clock stays on Tokyo. Product teams should treat IP-derived zone as marketing roughing and Intlas the user's stated preference until a calendar explicitly asks otherwise.
Daylight saving and the odd offsets that never go away
Jurisdictions keep revising DST rules. Some countries abolished seasonal shifts entirely; others moved transition weekends with short notice. That is why static offset tables in code rot. Non-integer offsets are normal: India uses UTC+5:30 year-round, Nepal UTC+5:45, Newfoundland UTC−3:30 with seasonal DST, and several Pacific islands use quarter-hour steps. Libraries that assume every zone is a whole hour are simply wrong.
Places that refuse a tidy UTC offset
| Location (IANA) | Standard offset | Observes DST |
|---|---|---|
| Asia/Kathmandu (Nepal) | UTC+5:45 | No |
| Asia/Kolkata (India) | UTC+5:30 | No |
| America/St_Johns (Newfoundland) | UTC−3:30 | Yes |
| Pacific/Chatham | UTC+12:45 | Yes |
| Australia/Lord_Howe | UTC+10:30 / +11:00 (seasonal) | Yes (30 min shift) |
| Australia/Eucla | UTC+8:45 | No |
Setting the timezone correctly on each OS
Wrong wall time almost always traces to manual override, dual boot, or VPN software that leaves the clock untouched while routing traffic elsewhere.
- Windows 11:Settings → Time & language → Date & time → Time zone (toggle automatic or pick a city).
- macOS:System Settings → General → Date & Time → Time zone map.
- GNOME Linux:Settings → Date & Time → Time Zone.
- iOS / Android:Settings → General → Date & Time (iOS) or System → Date & time (Android); enable network-provided time when possible.
Why timezone bugs still ship in 2026
Developers parse local midnight as if it were UTC midnight. Cron expressions run twice or skip an hour on DST boundaries. APIs return Z timestamps but the dashboard formats with the server zone instead of the viewer zone. Payment capture at 23:59 local can roll the settlement date. Fix pattern: store UTC instants, carry Asia/Tokyo style ids in profiles, and test with zones that have DST and fractional offsets.
Frequently asked questions
What is the difference between UTC and GMT?
For web scheduling they are effectively the same minute. UTC is defined from atomic clocks; GMT is a legacy civil label. Engineers say UTC in APIs; news sites still say GMT in headlines.
Why does my computer show the wrong time?
Automatic time disabled, wrong region picked, failed NTP sync behind a captive portal, or a dual-boot OS fighting hardware clock assumptions. Toggle network time, pick the correct city (not just offset), then reboot once.
What is an IANA timezone identifier?
A stable string like Europe/Berlin that maps to full rule history in the tzdb. Prefer it over fixed offsets in application code so political changes update with OS patches.
How many timezones are there in the world?
The IANA database contains hundreds of distinct zones because regions split rules even when offsets match today. The count is not the same as "24 hourly slices."
Why do some countries have half-hour offsets?
Historical and political choices: colonial rail timetables, staying aligned with neighbors while preserving solar noon, or avoiding two countries sharing identical clocks. India and Iran are textbook examples; fractional offsets are first-class data in tzdb.
Related tools
Network-derived geography (often mismatched with clock): What Is My Location. Public address for VPN checks: What Is My IP.
Sources cited above
- IANA Time Zone Database
- RFC 3339: Date and Time on the Internet
- ECMA-402 Intl.DateTimeFormat