Time Zone Converter

How time zone conversion works

Every place on earth keeps time as an offset from Coordinated Universal Time (UTC), the reference used by atomic clocks worldwide. Converting between two cities is a two-step subtraction: take the local time, remove its zone's offset to get UTC, then add the destination zone's offset. When New York is on UTC−5 and London is on UTC+0, the five-hour gap falls straight out of the arithmetic — 09:00 in New York is 14:00 in London.

The catch is that offsets are not constants. They change with daylight saving time, and each country runs on its own switch dates. That is why our converter pages always ask for (or default to) a specific date and apply the official IANA time zone database rules — the same rules your operating system uses — rather than a fixed hour difference.

Why the same conversion can change with the seasons

If you have ever scheduled a recurring call and had it drift out of sync twice a year, daylight saving time is the reason. Roughly 70 countries shift their clocks forward in spring and back in autumn — but on different dates. The United States switches in March and November; the European Union in late March and late October; most of Asia, Africa and South America never switches at all. In the weeks between one region's switch and another's, the time difference between them temporarily changes by an hour.

Abbreviations hide this trap: EST (UTC−5) and EDT (UTC−4) are the same place in different seasons. A meeting set as “3 PM EST” in July is ambiguous, because New York is actually on EDT then. Our converter sidesteps the ambiguity by using the IANA zone identifier (for example America/New_York), which encodes the full history of DST rules and picks the correct offset for the date you choose.

Not every zone is a whole hour

A quarter of the world's population lives on a non-hour offset. India keeps UTC+5:30, so Delhi is thirty minutes “off” from both its neighbours. Nepal uses UTC+5:45, Myanmar UTC+6:30, and parts of Australia (Adelaide, Darwin) UTC+9:30. The Chatham Islands of New Zealand sit at UTC+12:45 in local winter. If a conversion result ends in :15, :30 or :45, that is the correct answer, not a rounding glitch.

Choosing a time that works everywhere

For a call or video meeting, the goal is a slot where everyone is awake — ideally inside their 8 AM–9 PM window, and inside 9 AM–5 PM business hours if it is work. Useful rules of thumb:

• US ↔ Europe: late afternoon Europe pairs with morning US. 15:00 London is 10:00 New York and 07:00 Los Angeles.
• US ↔ Asia: there is almost no business-hours overlap; the least painful slots are early morning US / evening Asia, for example 08:00 New York = 18:00 Tokyo (next day, JST).
• Europe ↔ Asia: mornings Europe reach afternoon Asia comfortably — 10:00 London is 18:00 in Tokyo.
• India is the hinge: UTC+5:30 puts India within reach of both Europe (afternoon) and East Asia (morning), which is why so many global teams route through it.

Every pair page on this site shades the shared waking hours for you, and the meeting planner visualises a whole week for multiple cities at once. For a one-off check, the time difference table lists major cities side by side.