Time Zone Converter

Time zone conversion sits at the heart of modern remote work, cross-border finance, airline scheduling, satellite operations, telemedicine, and global supply chains. A correct converter must handle DST shifts (twice a year in roughly half the world), half-hour offsets (India, Iran, Newfoundland), forty-five-minute offsets (Nepal, the Chatham Islands), date-line crossings, and the occasional government decision to skip a day or change an offset overnight. This converter relies on the IANA Time Zone Database to handle all of that.

The IANA Time Zone Database was founded by Arthur David Olson at the National Institutes of Health in 1986. Olson released the source on Usenet under public-domain terms because he wanted Unix systems worldwide to interpret time consistently. By 2025 the database had grown to encode roughly 600 timezones with full historical rule sets going back to 1880, when standard time was first introduced in the United States. The database is now maintained collaboratively at iana.org/time-zones with releases roughly every three months.

Indian Standard Time has been the simplest case in the database since 1906. The Madras (now Chennai) Observatory standardised India on the 82.5 degrees east meridian, giving UTC+5:30 - a single timezone for a country 2,933 km wide. Before 1906, three civil times (Bombay Time at UTC+4:51, Madras Time at UTC+5:21, Calcutta Time at UTC+5:53) made railway timetables a nightmare. The Great Indian Peninsular Railway begged the colonial administration to unify, which it did on 1 September 1906.

US timezones, by contrast, were standardised by the Standard Time Act of 1918 signed by Woodrow Wilson, then complicated by the introduction and repeal of DST in 1918-1919, the 1942-1945 War Time period, the 1966 Uniform Time Act, and the 2007 Energy Policy Act extension. Hawaii skipped DST entirely. Most of Arizona stays on Mountain Standard Time year-round. Indiana had county-level DST chaos until 2006. The IANA TZDB encodes all of this in machine-readable rules.

Daylight Saving Time was popularised by the New Zealand entomologist George Hudson in 1895 and by the English builder William Willett in 1907. Germany adopted DST first on 30 April 1916 during the First World War coal crisis. The Russian Empire followed weeks later. The UK, France, and Italy in 1916; the US in 1918. Roughly half the world's population now observes some form of DST; the principal hold-outs are most of Asia, most of Africa, most of South America, and Hawaii plus most of Arizona.

Modern DST disputes continue in 2026. The European Union voted in 2019 to abolish the seasonal shift but has not implemented the decision pending member-state agreement on whether to lock the clock to standard or summer time. Several US states (Florida, California, Washington, Tennessee) have passed laws to keep DST year-round, pending federal authorisation under the Sunshine Protection Act. The IANA TZDB encodes the current law and is updated within weeks of any change.

This converter uses the browser's built-in Intl.DateTimeFormat API, which is the JavaScript binding to the underlying operating system's IANA TZDB. Every modern browser - Chrome, Firefox, Safari, Edge, Opera - ships with the same database. When governments change rules, the database update propagates through OS updates within weeks. The dual analog clocks on this page are correct as of the user's last system update, which for most users is within the past month.