About

Scheduling across timezones fails when you ignore Daylight Saving Time transitions. A meeting set for 14:00 UTC can land at different local hours depending on whether a region observes DST, and those rules change - the EU last adjusted in 2021, Morocco toggles mid-Ramadan. Static offset tables (UTC + 5) produce wrong results roughly 8 weeks per year for affected zones. This converter uses the browser's native Intl.DateTimeFormat engine, which resolves against the full IANA tz database (over 400 zones). Every offset is computed at the exact moment you query it, not from a lookup table. The time difference Δt between any two zones is derived from actual epoch math: t_A − t_B, where each value accounts for the zone's current UTC offset including DST state. Limitation: the tool relies on your browser's tz database version. Outdated browsers may lack recent political timezone changes (e.g., Volgograd's 2020 shift to UTC+4). For mission-critical scheduling, cross-reference with timeanddate.com.

Formulas

The time in zone B given a known time in zone A is computed as:

t_B = t_A + (O_B − O_A)

where t_A is the local time in zone A, O_A is the current UTC offset of zone A (in minutes), and O_B is the current UTC offset of zone B (in minutes). The offset O is DST-aware: it changes value at the exact transition instant defined by the IANA tz database rule for that zone.

The time difference between two zones:

Δt = O_B − O_A

A positive Δt means zone B is ahead. The UTC offset is extracted programmatically by formatting a reference date with Intl.DateTimeFormat using the timeZoneName: "shortOffset" option, then parsing the resulting string (e.g., "GMT+5:30" → 330 min).

Day/night classification uses solar approximation: local hour h where 6 ≤ h < 18 is daytime. This is a simplification; actual sunrise/sunset depends on latitude and date.

Reference Data

Timezone (IANA)	Common Name	Standard Offset	DST Offset	DST Period (approx.)
America/New_York	Eastern Time	UTC−5	UTC−4	Mar Sun2 → Nov Sun1
America/Chicago	Central Time	UTC−6	UTC−5	Mar Sun2 → Nov Sun1
America/Denver	Mountain Time	UTC−7	UTC−6	Mar Sun2 → Nov Sun1
America/Los_Angeles	Pacific Time	UTC−8	UTC−7	Mar Sun2 → Nov Sun1
America/Phoenix	Arizona (MST)	UTC−7	No DST	-
Europe/London	Greenwich / BST	UTC+0	UTC+1	Mar Sun−1 → Oct Sun−1
Europe/Berlin	Central European	UTC+1	UTC+2	Mar Sun−1 → Oct Sun−1
Europe/Moscow	Moscow Time	UTC+3	No DST	-
Asia/Dubai	Gulf Standard	UTC+4	No DST	-
Asia/Kolkata	India Standard	UTC+5:30	No DST	-
Asia/Kathmandu	Nepal Time	UTC+5:45	No DST	-
Asia/Shanghai	China Standard	UTC+8	No DST	-
Asia/Tokyo	Japan Standard	UTC+9	No DST	-
Australia/Sydney	AE Standard/Daylight	UTC+10	UTC+11	Oct Sun1 → Apr Sun1
Australia/Adelaide	AC Standard/Daylight	UTC+9:30	UTC+10:30	Oct Sun1 → Apr Sun1
Pacific/Auckland	New Zealand	UTC+12	UTC+13	Sep Sun−1 → Apr Sun1
Pacific/Chatham	Chatham Islands	UTC+12:45	UTC+13:45	Sep Sun−1 → Apr Sun1
Pacific/Honolulu	Hawaii Standard	UTC−10	No DST	-
Pacific/Marquesas	Marquesas Time	UTC−9:30	No DST	-
Etc/UTC	Coordinated Universal	UTC+0	No DST	-

Frequently Asked Questions

The converter delegates all offset resolution to the browser's Intl.DateTimeFormat API, which uses the IANA time zone database (tzdata). When you query a timezone at a specific moment, the API returns the offset that applies at that exact instant, including any DST shift. For example, America/New_York returns UTC−5 in January and UTC−4 in July. The tool never stores static offsets - every display tick recalculates.

Timezone offsets are political decisions, not astronomical ones. India adopted UTC+5:30 as a compromise between Kolkata (east) and Mumbai (west) longitudes. Nepal uses UTC+5:45 to distinguish itself from India. The Chatham Islands use UTC+12:45. This converter handles all fractional offsets natively because Intl.DateTimeFormat resolves them from the IANA database without rounding.

If you manually input a time that falls in a DST gap (the clock jumps from 2:00 AM to 3:00 AM), the JavaScript Date object typically rolls the time forward to the first valid moment (3:00 AM). The converter reflects whatever the browser's Date engine resolves. This is consistent with ECMA-262 specification behavior.

Yes. Governments can redefine their standard offset. Samoa jumped from UTC−11 to UTC+13 in 2011 to align with trading partners. Volgograd switched from UTC+3 to UTC+4 in 2020. Turkey permanently moved to UTC+3 in 2016. These changes are tracked in IANA tzdata updates, which browser vendors ship in engine updates. An outdated browser may not reflect recent political changes.

The indicator uses a simplified solar model: hours 06:00-17:59 local time are classified as day, and 18:00-05:59 as night. True sunrise and sunset depend on latitude, longitude, date, and atmospheric refraction. At high latitudes near solstices (e.g., Tromsø in June), the sun never sets, but the tool would still show a night icon after 18:00 local. Treat the indicator as a scheduling convenience, not an astronomical tool.

The Intl.supportedValuesOf('timeZone') method returns IANA timezone identifiers that the browser's ICU (International Components for Unicode) library supports. Chrome, Firefox, and Safari may ship different ICU versions. Older browsers may lack this method entirely, in which case the converter falls back to a curated list of 150+ common timezones. The core conversion math remains identical.