Time zone converter

Why the date matters, not only the time

The gap between two cities is not fixed. It moves when either of them changes its clocks, and they rarely change on the same day. Take 3:00 p.m. in London on three Mondays of 2026:

New York moved its clocks forward on 8 March and London not until 29 March, so for three weeks the two cities are four hours apart instead of five. Once London changes, it is an hour closer to Istanbul and Tokyo, which never change. Autumn repeats the trick: Europe goes back on 25 October 2026 and the US on 1 November, leaving one week with a four-hour gap.

That is why Octoolo asks for a date as well as a time, and works out each zone's offset for that moment.

Daylight saving rules around the world

• United States and most of Canada: clocks go forward on the second Sunday in March and back on the first Sunday in November. Most of Arizona stays on standard time all year.
• UK and the European Union: forward on the last Sunday in March, back on the last Sunday in October, at the same moment everywhere.
• Southern hemisphere: the seasons are reversed. Sydney goes back on 5 April 2026 and forward on 4 October 2026.
• No daylight saving: Japan, China, India and Turkey, among many others. Turkey has stayed on UTC+3 all year since 2016.

Some zones are not a whole number of hours from UTC: India is UTC+5:30 and Nepal UTC+5:45, so 15:00 UTC is 20:30 in Delhi and 20:45 in Kathmandu.

Governments change these rules from time to time, which is why the zone list follows the IANA time zone database, the record that phones and computers rely on, rather than a fixed table of offsets.

Cities, not abbreviations

Time zone abbreviations are ambiguous. CST can mean US Central Standard Time, China Standard Time or Cuba Standard Time, and IST is used for India, Ireland and Israel. EST is often written when EDT is meant, because people on the US East Coast say “Eastern” all year.

The IANA database avoids this by naming each zone after a region and a city that represents it: America/Chicago, Asia/Shanghai, Europe/Dublin. Each name carries that place's history of offsets and daylight saving rules, so the answer holds for past dates as well as future ones. Octoolo lists the zones Windows' browser engine knows, over 400 of them, under the names it uses (Asia/Calcutta rather than Asia/Kolkata, for instance); UTC is on the list from the start and cannot be added again once removed. When you are unsure which to pick, choose the zone named after the nearest large city in the same country. In the results, underscores show as spaces, so America/New_York reads America/New York.

Planning a call across time zones

• Set In to the organizer's zone and type the time they propose, then read everyone else's time from the list.
• Watch the weekday. Evening in New York is the next morning in Tokyo: 7:00 p.m. on Thursday 8 October 2026 is 8:00 a.m. on Friday there.
• For a weekly meeting, check the weeks around March and around late October and early November, when the gaps shift.
• Remember the date line. A call at 9:00 a.m. on Monday in Sydney is still Sunday afternoon in Los Angeles.
• Avoid the hours clocks skip or repeat. When New York goes back, 1:30 a.m. happens twice that night; when it goes forward, 2:30 a.m. never happens at all.
• Write times for servers, logs and flights in UTC, which never changes its clocks.

To turn a Unix timestamp from a log file into a readable date, use the Unix timestamp converter in the Dev Toolbox.