Time zones work as offsets from UTC (Coordinated Universal Time). Each
zone represents a fixed number of hours and minutes ahead of or behind
UTC — for example, New York is typically UTC−5 and Tokyo is UTC+9. When
you convert a time between two cities, you are essentially shifting the
clock by the difference between their two UTC offsets.
Daylight saving time complicates conversions. Many countries shift their
clocks forward by one hour in spring and back in autumn, meaning the
offset between two cities can change twice a year. London and New York
might be five hours apart in winter but only four in summer. A reliable
converter must know which DST rules apply to each city on the specific
date you are converting.
Clockr uses IANA timezone identifiers — such as "Europe/London" and
"America/New_York" — and the browser's Intl.DateTimeFormat API to
handle all daylight saving rules automatically for over 250 cities. The
IANA database contains the complete history of timezone changes for
every region, so your conversion stays accurate regardless of the date
you choose.
Frequently asked questions
How do I convert time between two countries?
Select your source city in the "From" dropdown and your destination
city in the "To" dropdown, then enter the date and time you want to
convert. Clockr instantly shows the equivalent local time in the
destination city, along with the UTC offsets and time difference.
Use the swap button to reverse the direction, or pick a common
conversion from the presets below the converter.
What is the difference between GMT and UTC?
GMT (Greenwich Mean Time) and UTC are practically identical for
everyday use — both represent offset zero. GMT is based on Earth's
rotation and was the original global standard centred on Greenwich,
London. UTC is based on atomic clocks and is the modern international
standard. The difference between them is less than a second. In
winter the UK uses GMT; in summer it switches to BST (UTC+1).
Which countries do not observe daylight saving time?
Many countries near the equator do not use DST because daylight
hours vary little year-round. Japan, China, India, South Korea, and
most of Africa and Southeast Asia do not observe it. In the United
States, Arizona (except the Navajo Nation) and Hawaii stay on
standard time year-round. Since 2024, Mexico has also stopped
observing DST in most regions.
What is the best time to schedule a meeting between the US and UK?
The overlap window depends on the season due to DST. When both
countries are on daylight saving, the gap is typically four to five
hours — meaning 9:00 AM Eastern in the US is 2:00 PM in London.
A practical meeting window is 9:00 AM to 12:00 PM Eastern (2:00 PM
to 5:00 PM UK time). Use Clockr to check the exact offset for your
specific meeting date.
How many hours ahead is Australia compared to the UK?
It depends on which Australian city and the time of year. Sydney
is typically 10 or 11 hours ahead of London — 11 hours during
Northern Hemisphere summer when London is on BST and Sydney is on
standard time, or 10 hours when both offsets align differently.
Perth is only 7 or 8 hours ahead. Always check the specific cities
and date in Clockr, as Australian states observe DST on different
schedules.
What time zone should I use for international business?
UTC is the standard reference for international business, aviation,
and computing — it avoids ambiguity about which country's daylight
saving rules apply. Many global companies schedule meetings in UTC
or specify times with the UTC offset (e.g. "14:00 UTC"). For
day-to-day work, convert to each participant's local time using a
timezone converter so nobody joins at the wrong hour.
Why does India have a half-hour time zone offset?
India uses a single time zone — IST (UTC+5:30) — across the entire
country, despite spanning nearly 30 degrees of longitude. The
half-hour offset was chosen in 1906 to place the standard meridian
near the centre of the country, roughly between western Gujarat and
eastern Assam. A single zone simplifies national scheduling, even
though solar noon varies by over an hour from east to west.
What is the time difference between New York and Los Angeles?
Los Angeles is three hours behind New York year-round. Both cities
observe daylight saving time on the same schedule, so the three-hour
gap stays constant — when it is noon in New York, it is 9:00 AM in
Los Angeles. Select both cities in Clockr's converter to see the
exact time for any date and time you enter.