Time Zone Converter

A Time Zone Converter takes a wall-clock reading in one place - 9:00 AM on 12 March in New York - and tells you what the clock says at that same instant somewhere else. It is not simple arithmetic, because the gap between two zones is not a constant. New York is five hours behind London for most of the year and four hours behind for part of it, and for two weeks in spring the gap is four hours because the United States changes its clocks before Europe does.

Conversions inside the United States are simpler. As an EST to CST time zone converter it shows Chicago one hour behind New York, and because Eastern and Central time change their clocks on the same dates, that one-hour gap holds through the year. Used as an Eastern and Central time zone converter for meeting planning, add Chicago to the planner strip next to New York, so a 9:00 AM Central stand-up reads as 10:00 AM Eastern at a glance. Pacific time runs three hours behind Eastern, and UTC is four or five hours ahead of Eastern depending on daylight saving.

This converter resolves every offset through the IANA time zone database that ships with your browser, evaluated at the specific instant you entered. That means daylight saving transitions, half-hour and quarter-hour offsets like India (UTC+05:30) and Nepal (UTC+05:45), and countries that have changed their rules are all handled by the same code path - nothing is hardcoded and nothing goes stale.

Alongside the conversion you get each zone's UTC offset and abbreviation for that date, the signed difference between the two, and a meeting-planner strip that lays the same instant across several zones at once so you can see which hour lands inside everybody's working day. Everything runs in your browser: no dates are uploaded, nothing is logged, and the tool keeps working offline once the page has loaded.

Time zones are political rather than geographic, and that is what makes them hard. Offsets change by government decree, sometimes with only weeks of notice, which is why the IANA database is updated several times a year and why any tool that hardcodes offsets eventually becomes wrong. Daylight saving is applied per instant rather than per zone here, which matters because the answer depends on the date you are converting, not on today: a meeting in March can land in a different offset than the same clock time in January, and the northern and southern hemispheres shift in opposite directions. Abbreviations are worse than useless for precision, since CST means three different things depending on whether you are in Chicago, Havana or Shanghai. Prefer the IANA zone name.