Coordinating with people in other countries is one of those small tasks that seems trivial until it goes wrong. A single DST rollover, an off-by-one on the date line, or a hidden assumption about someone’s local time can move a meeting by an hour or a full day. This time zone converter lets you pick any date and time in any zone and instantly see the equivalent moment in every other major city, using the up-to-date IANA Time Zone Database so DST transitions are handled correctly — even months into the future.

How time zones work

The Earth rotates 360° in roughly 24 hours, so each 15° longitude slice corresponds to one hour of solar time. In practice, political boundaries, economic ties, and historical accidents distort this neat picture: China uses a single time zone across a landmass that would naturally span five, India runs on a 30-minute offset (UTC+5:30), Nepal on a 45-minute offset (UTC+5:45), and some Pacific nations have chosen zones based on their trading partners rather than their longitude.

Everything is anchored to Coordinated Universal Time (UTC), the modern successor to Greenwich Mean Time. UTC does not observe Daylight Saving Time and is the reference point every other zone is defined against (e.g., UTC-5 for New York in winter, UTC-4 in summer).

Daylight Saving Time is where things break

Most scheduling bugs trace back to DST. The spring-forward and fall-back dates are not synchronized across the world:

North America switches on the second Sunday of March and the first Sunday of November.
Europe switches on the last Sunday of March and the last Sunday of October.
Australia (which is in the Southern Hemisphere) runs DST from October to April — the opposite of the North.
Japan, India, China, and most of Africa do not observe DST at all.

That means there are two weeks every March and two weeks every October when the gap between London and New York is four hours, not the usual five, because one region has switched and the other hasn’t yet. A recurring 3 PM London meeting silently moves to 10 AM or 11 AM in New York depending on the week.

This tool uses the IANA database, which tracks every current and historical DST rule, so the conversion stays correct across any transition.

How to use this tool

Pick the source date and time using the date picker.
Choose the source time zone (the tool defaults to your browser’s local zone).
Review the converted time in London, New York, Los Angeles, Tokyo, Sydney, and other major hubs.
For a custom list, select any IANA zone from the dropdown.

Worked example

You are in Tallinn (Europe/Tallinn, UTC+3 in summer / UTC+2 in winter) and want to set up a recurring weekly call with colleagues in San Francisco (America/Los_Angeles) for 10:00 Tallinn time.

Summer (EET+DST vs PT+DST, 10-hour gap): 10:00 Tallinn = 00:00 San Francisco. Too early.
Winter (EET vs PST, also 10-hour gap): 10:00 Tallinn = 00:00 San Francisco. Same.
Two transition weeks in March and November: the gap briefly becomes 11 hours. The 10:00 slot shifts to 23:00 the previous day for SF.

The fix is to schedule 17:00 Tallinn / 07:00 San Francisco instead, which stays within the overlap of “late afternoon Europe / early morning US West Coast” all year round.

Tips for international scheduling

Always state the zone explicitly when sending invites (“3 PM CET” not “3 PM”). Calendar apps generally handle DST correctly, but only if the underlying event was created with a zone, not a floating local time.
Watch the date line. A Thursday 22:00 call in New York is already Friday 11:00 in Tokyo and 13:00 in Sydney.
Identify the “golden window”. For teams split across Europe and North America, 13:00–16:00 UTC usually catches late morning in the Americas and late afternoon in Europe.
Beware half-hour and 45-minute zones. India is 30 minutes off, Nepal 45 minutes, parts of Australia 30 minutes. If you casually “round” to the nearest hour, you will be wrong.
Pin recurring meetings to a canonical host. Pick one person whose local time anchors the meeting; everyone else’s time floats with DST and travel.

Frequently asked questions

Why does my converted time look one hour off around March or November?

You are almost certainly looking at a DST transition week. For about two weeks each spring and fall, the gap between European and North American zones changes because the regions switch on different dates. The converter uses the current IANA rules, so the result is correct — it is the mental model of “always 5 hours” that is wrong.

What is the difference between GMT and UTC?

In everyday use they are treated as the same. Technically, UTC is a time standard defined by atomic clocks with occasional leap-second adjustments, while GMT is a time zone historically tied to the solar time at Greenwich. Most software, including this tool, uses UTC internally.

Which zone should I use for servers and databases?

Store timestamps in UTC and convert only at the display layer. Storing local time with a zone string is possible but causes an endless series of edge cases around DST transitions (e.g., 02:30 on the fall-back night happens twice). UTC has no DST and no ambiguity.

Do all countries observe DST?

No. Most of Asia, most of Africa, the equatorial regions, and a growing number of European regions have abolished or paused DST. The EU has repeatedly discussed ending it but has not yet acted. Russia, Turkey, and Iceland already run on permanent standard time.

What happens to my invite when the other country abolishes DST mid-year?

If you’re using a calendar like Google Calendar or Outlook, updates to the IANA database flow through within days and recurring events shift automatically. That is why storing events with a zone name (e.g., Europe/Tallinn) rather than a fixed UTC offset matters.

Privacy note

The conversion happens entirely in your browser using the JavaScript Intl.DateTimeFormat and the zone data shipped with it. No dates, times, or zone choices leave your device.

Time Zone Converter