Time Zone Converter
Convert a date and time between two cities using IANA time zone rules, including daylight saving time on the chosen date.
Updated Formula covered by automated tests
Choose a date, a clock time and two places, and the converter shows the matching local time at the other end, the UTC offset each place uses on that particular date, and whether the result falls on the previous or next calendar day. A live clock for both places runs underneath.
The date field is there for a reason. Most of North America, Europe, and parts of South America and Oceania shift their clocks for daylight saving time, but not on the same weekends, and the southern hemisphere shifts in the opposite season. The gap between New York and London is five hours for most of the year, four hours for a few weeks each spring and one week each autumn, and a converter that ignores the date will be wrong during those windows.
Typical uses are scheduling a video call across continents, reading a webinar time listed in another zone, checking when a product launch or sports final airs locally, or telling a colleague abroad when you will be online.
The formula
- offset₁(date), offset₂(date)
- UTC offset of each place in hours and minutes on that date, including daylight saving time when it is in force (for example −5:00 for New York in winter, −4:00 in summer)
- UTC
- Coordinated Universal Time, the reference time scale kept by atomic clocks and coordinated by the BIPM
- local time₁, local time₂
- Wall-clock time in the starting place and the destination
Every civil time zone is defined as an offset from UTC, but the offset is a rule rather than a constant: it depends on the date and on decisions by each government. The calculator looks offsets up in the IANA time zone database (the "tz" database built into every modern browser and operating system), which records the daylight-saving rules and their historical changes for each region, identified by names like America/New_York or Asia/Kolkata.
Since 2007 the United States moves clocks forward on the second Sunday in March and back on the first Sunday in November. The European Union and the UK change on the last Sunday of March and of October. In 2026 that means the US springs forward on March 8 while London waits until March 29, so for three weeks New York is only four hours behind London.
Some local times do not exist or happen twice. On the night clocks spring forward, 2:30 a.m. never occurs in New York, and the converter reads it as 3:30 a.m. daylight time; on the night they fall back, 1:30 a.m. happens twice and the first occurrence is used.
Worked example
A product team in New York holds a stand-up at 9:00 a.m. on Tuesday, March 10, 2026 and wants to tell its London designer what time to join.
- 1 New York switched to Eastern Daylight Time on March 8, so its offset on March 10 is UTC−4.
- 2 Convert to UTC: 9:00 − (−4:00) = 13:00 UTC.
- 3 London stays on Greenwich Mean Time until March 29, so its offset is UTC+0.
- 4 Convert to London time: 13:00 + 0:00 = 13:00, the same calendar day.
- 5 Check: the difference is 0 − (−4) = 4 hours, one hour less than the 5-hour gap on March 2 or March 31.
Result: The designer should join at 1:00 p.m. London time. On any date after March 29 the same 9:00 a.m. meeting is at 2:00 p.m. in London.
Before you rely on the result
- Results depend on the time zone data shipped with your browser. If a government changes its rules at short notice, an outdated browser can be wrong until it updates.
- The list covers major cities. Places in the same country can use different rules (Arizona and Indiana have both had exceptions), so pick the city closest to the person you are meeting.
Frequently asked questions
Is GMT the same as UTC?
For scheduling, yes: both are offset zero. Technically UTC is an atomic time scale and GMT is a time zone name used by the UK and some West African countries in winter. London is not on GMT in summer; it uses British Summer Time, UTC+1.
Which places do not use daylight saving time?
Hawaii, most of Arizona (the Navajo Nation is the exception), and US territories such as Puerto Rico and Guam stay on standard time all year. So do Japan, China, India and most countries near the equator. Choose Phoenix in the list to see Arizona’s fixed UTC−7.
Why does India have a half-hour offset?
India uses a single zone, UTC+5:30, roughly centered on the longitude of the country. Other non-hour offsets exist too: Newfoundland is UTC−3:30 in winter and Nepal is UTC+5:45. The converter handles these because it works in minutes, not whole hours.
When I convert an evening time to Asia, why does the date change?
Places far east of you are already into the next day. 6:00 p.m. on October 18 in Los Angeles (UTC−7) is 01:00 UTC on October 19, which is 10:00 a.m. on October 19 in Tokyo (UTC+9). The +1 Day badge flags that shift.
Sources
- IANA Time Zone Database (iana.org)
- NIST: Daylight Saving Time (nist.gov)