The hardest kind of shift, over the longest kind of flight
London to Tokyo combines the two things that make jet lag worst: a large time difference and the difficult eastbound direction. Tokyo runs nine hours ahead of London (eight when the UK is on British Summer Time), and the flight is a long one — around 14 hours non-stop. You leave London around lunchtime and land in Tokyo the following morning, having crossed most of the planet while your body clock stays stubbornly on UK time.
Because you're flying east, your body has to *advance — go to bed and wake up earlier — and that's the direction it resists. Land in Tokyo at 9am and your London clock reads midnight; you're being asked to start a Japanese day at what your body considers the start of the night. This is a route where casual improvisation fails and a plan pays off enormously. Handled well, you can be reasonably functional within a few days; handled badly, it can shadow an entire week-long trip.
Which way is your body actually shifting?
Here's a quirk worth understanding: a nine-hour eastward shift is close to the halfway point of the 24-hour clock, and your body will sometimes find it easier to adjust by going the "long way round" — delaying 15 hours westward rather than advancing 9 hours eastward. In practice, for a nine-hour eastbound trip like London to Tokyo, most people still do best treating it as an advance and chasing morning light in Tokyo. But it's why this particular shift can feel unpredictable, and why a personalised plan that does the maths for your exact flight and stopover is genuinely useful here.
For most travellers, the working strategy is: pull your clock earlier — earlier light, earlier sleep — while being careful to avoid light at the wrong times, which on a shift this large can actively push you the wrong way.
Before you fly: start the advance early
A shift this large is far more manageable if you've already banked some of it before departure. For the three or four nights before you fly, go to bed an hour earlier each night and get up an hour earlier, chasing bright light immediately on waking. Morning light is your strongest tool for advancing the clock. In the evenings, dim the lights early and avoid screens so melatonin can rise sooner.
Even shifting two or three hours earlier before departure turns a nine-hour mountain into a six-hour hill. On the toughest routes, pre-flight preparation is the single highest-value thing you can do.
On the flight: sleep on Tokyo's clock
The London to Tokyo flight straddles both clocks, so the key is to sleep during the portion that corresponds to Tokyo's night, not London's.
Set your watch to Tokyo time at boarding and think in Tokyo time for the rest of the journey. Because you land in the Tokyo morning, you want to arrive having slept during the back half of the flight — that's Tokyo's night. Early in the flight (Tokyo daytime), stay awake: eat, watch films, keep the light on. Then, as it becomes Tokyo evening, shut it all down — eye mask, earplugs, cabin dimmed — and sleep as much as you can. A low dose of melatonin timed to Tokyo bedtime can help you fall asleep and reinforce the eastward shift, but check with a pharmacist first. Stay well hydrated across the whole 14 hours; the dry cabin makes everything worse.
Your first 48 hours in Tokyo
Arrival morning. You'll land into a Tokyo morning with your body convinced it's the middle of the night. This is the crux moment. Do not go to the hotel and sleep — that's the single most common mistake, and it can set your recovery back days. Get outside into morning light, which is precisely what an eastbound arrival needs. Eat breakfast on Tokyo time. Keep moving. If you're truly unable to function, cap any nap at 20 minutes before early afternoon.
A subtlety for very large shifts. On a nine-hour eastbound shift, blasting yourself with light at the wrong end of the day can backfire and delay you further. In the first day or two, the safe general approach is to seek light in the Tokyo late morning and midday and avoid bright light in the very early Tokyo morning hours. This is exactly the kind of nuance a personalised plan handles precisely — the timing that helps on day one is slightly different from day three.
Evening. Push through to a Tokyo bedtime of around 9–10pm. Eat dinner on local time. Wind down with dim light. You'll likely sleep hard from exhaustion, then wake in the small hours — that's normal on the first couple of nights. Keep the room dark and rest rather than getting up.
First full day. Wake by 7am, get bright morning light and a walk. Keep caffeine to the morning. Each day the middle-of-the-night waking should shrink. Because this is a large shift, give yourself grace — full adjustment can take the best part of a week, but you'll be usably functional well before then.
Seasons in Tokyo
Tokyo has four distinct seasons and fairly stable day length compared to London — summer days run to about 14.5 hours and winter days to around 9.5, without London's extremes. Summers are hot and humid, which can compound fatigue, so factor in air-conditioned rest during the day's peak heat without turning it into a long nap. Winter days are crisp and clear with reliable morning sun — helpful for the morning-light strategy an eastbound arrival depends on.
The bottom line
London to Tokyo is one of the harder mainstream jet lag routes: a nine-hour shift in the difficult eastbound direction over a 14-hour flight. The three things that matter most are starting your advance a few days before departure, sleeping during Tokyo's night on the flight, and being precise — not just aggressive — with light on arrival, because on a shift this large, light at the wrong time can set you back. Give it a real plan and you'll reclaim most of your trip.