Flying east vs west

Updated 2026-08-17

East is harder, and it isn’t in your head. Westward travel asks your body to do what it already wants to; eastward asks for the opposite. Same number of zones, roughly half again the recovery time.

Why the asymmetry exists

Left alone in constant conditions, human circadian rhythm runs a little longer than 24 hours. Every day your body is mildly inclined to drift later.

Flying west lengthens your day. You’re going downhill: about 1.5 hours a day, more if you’re a night owl.
Flying east shortens it. Uphill, against the drift: about 1 hour a day, less if you’re an owl.

That’s why a five-hour hop to New York from London feels survivable and the same five hours back feels like a week.

The long way round

A clock is a circle, so there are always two routes to the same destination time. To reach a place ten hours ahead you can pull yourself 10 hours earlier, or push yourself 14 hours later.

The second sounds mad — four more hours of shifting — but you cover it at 1.5 hours a day instead of 1:

Advancing 10 h ≈ 10 nights
Delaying 14 h ≈ 9 nights

It also feels easier the whole way, because every night is a late night rather than a nightly fight to fall asleep before you’re tired.

Which to choose

Zones east	Usually best
1–6	Advance — an hour a night, starting a few days out
7–9	Depends on chronotype: owls should consider delaying
10+	Delay. Stay up progressively later instead

Ray costs both directions in nights and picks the cheaper one for your chronotype, which is why a Tokyo trip sometimes tells you to stay up late rather than go to bed early.

Practical notes for each direction

Going east: morning light after CBTmin, dim evenings, melatonin five hours before your target bedtime, last coffee six hours before it.

Going west: sunglasses for the first hours after waking, bright light in the late afternoon and evening, and caffeine is a legitimate tool for holding out until the local bedtime.