Why flying east is harder

Ask frequent travellers which direction is worse and most will say east without hesitating. They are right, and it is not a matter of temperament or which trips happen to have been stressful. The asymmetry is built into how the body clock works, and it is predictable enough to plan around.

The clock runs long

Left with no external cues, the human circadian rhythm does not hold to exactly twenty-four hours. For most people it runs slightly longer — the internal day is a little more than the real one.

That means the clock is always being corrected slightly earlier by daylight, every day of your life, just to stay in step. Its natural tendency is to drift later. And a system whose natural tendency is to drift later finds one of the two possible corrections much easier than the other:

• Delaying — going to bed later, getting up later — runs with the drift. The clock is being asked to do more of what it already wants.
• Advancing — going to bed earlier, getting up earlier — runs against it. The clock is being asked to give up ground it naturally gains.

Flying west asks you to delay. Flying east asks you to advance. That is the whole of it.

What it costs in days

The practical consequence is that the same number of time zones takes longer to absorb eastbound than westbound. A shift that resolves in a few days flying west can take meaningfully longer flying east — the clock simply moves less per day in the harder direction.

There is also a nastier failure mode that only occurs going east. With a large enough eastward shift, the body sometimes gives up on advancing and goes the long way round on its own — delaying by sixteen hours rather than advancing by eight, arriving at the same clock position from the opposite side. Unplanned, that is the slowest possible route, with a stretch in the middle where every light instruction written for an advance is pointing the wrong way.

The defence for shifts up to nine hours is the same as the defence against most jet-lag problems: control the light, and start before you fly. For eastbound shifts of ten hours or more, Jetlag Away plans the long way round deliberately — delaying by the rest of the day, at the delaying rate, with the light timed for a delay from the first morning. How a plan is built has the threshold and the reasoning, and the plan itself tells you when it has done this.

Why the flight itself feels different

The direction changes what a long flight is for, which is why sensible in-flight advice is not symmetrical.

Flying east, you are usually leaving in the evening and arriving in the morning. You need to sleep on the plane, because you are landing into a day that your body thinks is the middle of the night, and the sleep you get in the air is the only sleep that day gets. Jetlag Away’s eastbound plans put the sleep window where the destination’s night falls in the flight — usually the later part — and ask you to stay awake and in the light before it, treating the window as a genuine night’s sleep rather than a nap you might get around to.

Flying west, you are usually arriving into an afternoon or evening that your body thinks is already night. The task is not to sleep but to stay up, sometimes for several hours past when you want to. So the plan keeps you awake and in the light for the flight wherever it can, because staying awake later is exactly the delaying signal you want — and inserts a short rest only when the day would otherwise run past twenty-four hours before your first local bedtime.

This is why “sleep on the plane” is bad advice half the time. It is excellent advice going east and often counterproductive going west.

The trip that is not worth adjusting for

If you are flying east for two or three days and flying home again, adjusting fully may be the wrong goal. You would spend the whole trip in the hard direction and then have to undo it, and you may well end up jet-lagged twice for the sake of a trip you were never awake for.

Staying substantially on home time — scheduling what you can within it, protecting sleep, and accepting that some hours will be awkward — is a legitimate strategy for a short eastbound trip. It is not what most jet-lag advice tells you, because most jet-lag advice assumes adjustment is always the objective.

What actually helps going east

The direction is fixed; how much of it you face on arrival is not.

• Pre-shift before you go. Moving your sleep schedule earlier in the days before an eastbound flight is the single most effective thing available, because it converts the hard adjustment into smaller pieces spread over days when you are at home and in control of your light. Jetlag Away moves your sleep window earlier on the last nights before you fly — never by more than an hour a night, because advancing the schedule faster does not advance the clock faster — up to a total of an hour and a half on gentle, three hours on moderate and four on aggressive, within the limits you set. Each of those nights comes with a morning light window, which is the part that makes the earlier bedtime count.
• Get the morning light right, and get it outside. Advancing needs light after your body’s temperature minimum, which for an eastbound traveller means genuine morning daylight at the destination — not a lit room.
• Protect the evening. Late light delays, which is the opposite of what you need. This is the half people forget.
• Do not treat naps as free. Sleeping off-schedule feeds the rhythm you are trying to move. Jetlag Away’s gentle and moderate plans allow short naps as a comfort trade; the aggressive plan removes them entirely, deliberately.

Light timing covers the mechanism in more detail, and how a plan is built describes how the app turns a flight into a schedule.

Jetlag Away is a scheduling tool and not medical advice. If you have a sleep or circadian disorder, or any diagnosed condition affected by sleep, talk to a healthcare professional first — see the health disclaimer in our terms.