Why Time Differences Between Cities Change Throughout the Year
Why London and New York are sometimes 5 hours apart and sometimes 4, due to asynchronous Daylight Saving Time switches.
A frequent misconception is that the time difference between two cities is a fixed mathematical constant. In reality, the difference between London and New York fluctuates between 4 and 5 hours twice every year.
This happens because North America and Europe transition to Daylight Saving Time on different weekends. The United States moves clocks forward on the second Sunday in March and back on the first Sunday in November. The European Union moves clocks on the last Sunday in March and the last Sunday in October. During these 2-to-3 week transitional windows, team meeting schedules that worked smoothly can suddenly shift by an entire hour.
Experience this phenomenon in real time
Test daylight transitions, fractional offsets, and team availability on our interactive instrument.
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