Key facts Daylight saving time changes the gap on most routes by 1 hour for part of the year. Across the date line (for example LA to Tokyo), the clock difference is large but the body feels a smaller westward shift. East shifts take roughly 1 day per hour; west shifts a bit less. Make a plan for your trip
How big is the time difference on popular routes? From New York Route July January Body-clock shift Days to adjust (2-day head start) London +5 h +5 h 5 hours earlier 5 (3) Paris +6 h +6 h 6 hours earlier 6 (4) Rome +6 h +6 h 6 hours earlier 6 (4) Dublin +5 h +5 h 5 hours earlier 5 (3) Barcelona +6 h +6 h 6 hours earlier 6 (4) Lisbon +5 h +5 h 5 hours earlier 5 (3) Amsterdam +6 h +6 h 6 hours earlier 6 (4) Madrid +6 h +6 h 6 hours earlier 6 (4) Athens +7 h +7 h 7 hours earlier 7 (5) Reykjavík +4 h +5 h 4 hours earlier 4 (2) Tokyo +13 h +14 h 11 hours later 8 (6) Seoul +13 h +14 h 11 hours later 8 (6) Honolulu −6 h −5 h 6 hours later 4 (3)
From Los Angeles Route July January Body-clock shift Days to adjust (2-day head start) London +8 h +8 h 8 hours earlier 8 (6) Paris +9 h +9 h 9 hours earlier 9 (7) Rome +9 h +9 h 9 hours earlier 9 (7) Tokyo +16 h +17 h 8 hours later 6 (4) Seoul +16 h +17 h 8 hours later 6 (4) Sydney +17 h +19 h 7 hours later 5 (4) Auckland +19 h +21 h 5 hours later 4 (2) Honolulu −3 h −2 h 3 hours later 2 (1) Cancún +2 h +3 h 2 hours earlier 2 (1)
From Denver Route July January Body-clock shift Days to adjust (2-day head start) London +7 h +7 h 7 hours earlier 7 (5) Paris +8 h +8 h 8 hours earlier 8 (6) Rome +8 h +8 h 8 hours earlier 8 (6) Dublin +7 h +7 h 7 hours earlier 7 (5) Tokyo +15 h +16 h 9 hours later 6 (5) Honolulu −4 h −3 h 4 hours later 3 (2) Cancún +1 h +2 h minimal —
From Chicago Route July January Body-clock shift Days to adjust (2-day head start) London +6 h +6 h 6 hours earlier 6 (4) Paris +7 h +7 h 7 hours earlier 7 (5) Dublin +6 h +6 h 6 hours earlier 6 (4) Rome +7 h +7 h 7 hours earlier 7 (5) Tokyo +14 h +15 h 10 hours later 7 (6)
From San Francisco Route July January Body-clock shift Days to adjust (2-day head start) London +8 h +8 h 8 hours earlier 8 (6) Paris +9 h +9 h 9 hours earlier 9 (7) Tokyo +16 h +17 h 8 hours later 6 (4) Seoul +16 h +17 h 8 hours later 6 (4) Sydney +17 h +19 h 7 hours later 5 (4)
From Seattle Route July January Body-clock shift Days to adjust (2-day head start) London +8 h +8 h 8 hours earlier 8 (6) Tokyo +16 h +17 h 8 hours later 6 (4) Paris +9 h +9 h 9 hours earlier 9 (7) Honolulu −3 h −2 h 3 hours later 2 (1)
From Boston Route July January Body-clock shift Days to adjust (2-day head start) London +5 h +5 h 5 hours earlier 5 (3) Dublin +5 h +5 h 5 hours earlier 5 (3) Paris +6 h +6 h 6 hours earlier 6 (4) Rome +6 h +6 h 6 hours earlier 6 (4) Lisbon +5 h +5 h 5 hours earlier 5 (3)
From Miami Route July January Body-clock shift Days to adjust (2-day head start) London +5 h +5 h 5 hours earlier 5 (3) Paris +6 h +6 h 6 hours earlier 6 (4) Madrid +6 h +6 h 6 hours earlier 6 (4) Barcelona +6 h +6 h 6 hours earlier 6 (4) Rome +6 h +6 h 6 hours earlier 6 (4)
From Dallas Route July January Body-clock shift Days to adjust (2-day head start) London +6 h +6 h 6 hours earlier 6 (4) Tokyo +14 h +15 h 10 hours later 7 (6) Paris +7 h +7 h 7 hours earlier 7 (5)
From Atlanta Route July January Body-clock shift Days to adjust (2-day head start) London +5 h +5 h 5 hours earlier 5 (3) Paris +6 h +6 h 6 hours earlier 6 (4) Rome +6 h +6 h 6 hours earlier 6 (4)
From Houston Route July January Body-clock shift Days to adjust (2-day head start) London +6 h +6 h 6 hours earlier 6 (4) Tokyo +14 h +15 h 10 hours later 7 (6)
From Washington, DC Route July January Body-clock shift Days to adjust (2-day head start) London +5 h +5 h 5 hours earlier 5 (3) Paris +6 h +6 h 6 hours earlier 6 (4)
From London Route July January Body-clock shift Days to adjust (2-day head start) New York −5 h −5 h 5 hours later 4 (2) Orlando −5 h −5 h 5 hours later 4 (2)
From Sydney Route July January Body-clock shift Days to adjust (2-day head start) London −9 h −11 h 9 hours later 6 (5)
Frequently asked questions Why is the time difference different in winter? Most US and European cities use daylight saving time but switch on different dates, and many destinations (Japan, Hawaii, Iceland, Mexico's Cancún) do not use it at all.
What does "body-clock shift" mean? The number of hours your internal clock must move, earlier or later. Across the date line it is smaller than the clock difference.
More guides Sources How we turn this research into plans: methodology .
Not medical advice. General sleep and travel guidance based on published circadian research. Ask your doctor or pediatrician about melatonin or other supplements, pregnancy, medications or health conditions. Never give melatonin to babies or toddlers.