World Clock Calculator
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Reviewed by Daniel Agrici, Founder & Lead Developer
Formula
Target Time = Source Time + (Target UTC Offset - Source UTC Offset)
To convert between time zones, add the difference between the target and source UTC offsets to the source time. If the result exceeds 24 hours, add one day. If it falls below 0, subtract one day.
Worked Examples
Example 1: US-Europe Business Call
Problem:A team in New York wants to schedule a call with London colleagues at 2:00 PM New York time. What time is it in London?
Solution:New York is UTC-5, London is UTC+0\nTime difference = 0 - (-5) = +5 hours\n2:00 PM + 5 hours = 7:00 PM\n\nLondon is 5 hours ahead of New York.\nNote: During summer when both observe DST, the difference remains 5 hours since both shift by 1 hour.
Result:2:00 PM in New York = 7:00 PM in London (5 hours ahead)
Example 2: US-Japan Coordination
Problem:A developer in Los Angeles needs to join a 10:00 AM meeting in Tokyo. What time must they wake up?
Solution:Los Angeles is UTC-8, Tokyo is UTC+9\nTime difference = 9 - (-8) = +17 hours\n10:00 AM Tokyo - 17 hours = 5:00 PM previous day LA time\n\nAlternatively: Tokyo is 17 hours ahead of LA.\nSo 10 AM Tuesday in Tokyo = 5 PM Monday in LA.
Result:10:00 AM Tokyo = 5:00 PM previous day in Los Angeles (17 hours behind)
Frequently Asked Questions
How do time zones work around the world?
Time zones divide the Earth into 24 regions, each nominally spanning 15 degrees of longitude, corresponding to one hour of time difference. The system is based on Coordinated Universal Time (UTC), formerly Greenwich Mean Time (GMT), centered on the Prime Meridian at Greenwich, London. Moving east from Greenwich, time zones are ahead (UTC+1, UTC+2, etc.), and moving west they are behind (UTC-1, UTC-2, etc.). However, actual time zone boundaries follow political and geographical borders rather than strict longitude lines, which is why some countries and regions have unusual offsets. India uses a single time zone of UTC+5:30 despite spanning about 30 degrees of longitude.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy