Timezone Converter

Timezone reference

Everything you need to read a timestamp, schedule a cross-continent meeting, or debug a log line in the wrong zone — abbreviations, UTC offsets, DST quirks, and the gotchas that bite teams every quarter.

Timezone abbreviation cheat sheet

Abbreviations look unambiguous but rarely are. IST means India Standard Time, Israel Standard Time, or Irish Standard Time depending on context. CST is American Central, China Standard, orCuba Standard. The picker in the calculator above asks you to choose when there's overlap.

UTC vs GMT: are they the same?

Almost. For practical purposes they're identical (both +00:00). The technical difference: UTC is a time standard maintained by atomic clocks with leap seconds inserted periodically; GMT is a timezone based on the mean solar time at the Greenwich meridian. Software, APIs, and standards use UTC. Daily life and the UK (in winter) use GMT. Use UTC in code.

Why daylight saving time is a footgun

Twice a year, regions that observe DST shift their clocks one hour. The consequences:

• A recurring meeting "at 9 AM EST" silently becomes 9 AM EDT in March — the absolute UTC instant changes, so participants in non-DST zones (India, China, Japan) see the meeting move by an hour.
• Some local times don't exist on DST-spring-forward days (e.g., March 8, 2026 in the US: 02:00–02:59 EST is skipped). Cron jobs scheduled for that hour fire 0 or 2 times depending on the implementation.
• Some local times happen twice on DST-fall-back days. Logs with naked local timestamps are ambiguous during that hour — always log in UTC.
• Australia's east coast and New Zealand are in the southern hemisphere, so their DST schedule is opposite to the US/EU. AEDT runs Oct–Apr.
• India, China, Japan, most of Africa, most of South America never observe DST. Arizona and Hawaii stay on standard year-round.

See the DST 2026 schedule table above for exact transition dates by region.

Quick conversion math

For the most common pairs, the offsets are stable enough to do mentally:

• EST → IST: add 10:30 hours (9:30 during US DST)
• EST → PST: subtract 3 hours (always — both observe DST together)
• EST → GMT: add 5 hours (4 during US DST)
• IST → GMT: subtract 5:30 hours
• JST → GMT: subtract 9 hours (no DST in Japan, stable year-round)
• UTC → JST: add 9 hours
• PST → AEDT: add 19 hours (or 18, depending on DST overlap)

Best practices for systems

• Store everything in UTC.Convert at display time, based on the user's timezone preference.
• Use IANA names, not abbreviations."America/New_York" is unambiguous; "EST" isn't.
• Log timestamps in ISO 8601 with a Z or offset. Naked datetimes are ambiguous; 2026-05-18T12:00:00 can mean any of 24 different absolute moments.
• Don't hard-code DST rules.Use the OS's tzdata (IANA) — it's updated when governments change DST policies.
• Test around DST transitions. Spring forward, fall back, leap years, and zones that change DST policy mid-year (rare but real, e.g. Syria 2022, Mexico 2022) are all classic edge cases.
• Watch for fractional offsets. India (+05:30), Nepal (+05:45), Newfoundland (−03:30), some parts of Australia (+09:30/+10:30). Code that assumes whole-hour offsets breaks here.

Standards & references

• IANA Time Zone Database (tzdata) — the canonical source for zone identifiers and DST rules. Updated several times per year.
• ISO 8601 — international standard for date and time representations (the 2026-05-18T12:00:00Z format).
• RFC 3339 — Internet-friendly profile of ISO 8601, used by most JSON APIs.
• Unix time— seconds since 1970-01-01T00:00:00Z, defined in POSIX. Will overflow signed 32-bit on 2038-01-19T03:14:07Z (the “Year 2038 problem”).