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🇬🇧 → 🇯🇵 London to Tokyo jet lag: what to expect and how to adjust
How bad is jet lag on this route?
The time difference between London and Tokyo is about 9 hours (it varies with daylight saving time), and the flight takes about 12–14 hours. Without a strategy, expect roughly 10 days for your body to settle into local time. Pre-trip shifting and well-timed light can make those days much easier.
Which way does your body clock shift?
The time difference is so large that shifting your clock later (about 1.5 hours per day) is usually the easier way around. Research on eastward trips over 8 time zones shows most people’s clocks naturally adjust in this "backwards" direction.
Light timing matters most
Bright light is the strongest lever for moving your body clock — but light at the wrong time moves it the wrong way. After large eastward hops, the standard advice is to avoid bright morning light for the first days and seek light only after your body temperature minimum (about 3 hours before your usual wake time). The planner computes these seek/avoid windows for each day.
Caffeine and naps
Cut caffeine 6 hours before your target bedtime — a controlled study found even a dose 6 hours out shortened sleep by about an hour. If you must nap, keep it to 20–30 minutes and not in the late afternoon.
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