Jet Lag: East Is Harder, or Does It Just Feel That Way?

The physiological rule — and why travellers mostly contradict it

Start with the number, because it is well sourced and it is not the whole story. The CDC’s Yellow Book puts average adaptation at 1 hour per day traveling east and 1.5 hours per day traveling west. That asymmetry is not a hunch; it follows from the body’s intrinsic circadian period being slightly longer than 24 hours, so every human naturally drifts later each night. Delaying your clock goes with that grain; advancing it fights it. On that basis, eastbound should be the harder direction — and the common claim that the westward stretch of the day is what wrecks you is backwards.

Now the part that complicates it, which is the most useful thing on this page. Traveller reports broadly say the opposite: that the return leg is worse, and that it is the westward return home. This is not a handful of complaints. On a long-running Rick Steves forum thread on exactly this question, the majority of posters describe arriving somewhere fine and then enduring weeks of 4am waking after flying home. One nine-hour Europe return is reported as “7 nights before I could sleep 8 hours… two weeks until I could sleep until 6am.” Another poster, on a westbound return, is “still waking up at 4:30 for two weeks.” Others in the same thread say the reverse — that Europe-bound eastbound is worse for them.

Both are published here rather than resolved by picking the side I like. The most likely reconciliation is that adaptation rate and lived difficulty are not the same measurement. The CDC figure describes how fast the clock re-entrains when you commit to the local schedule. What the forum posters describe is a failure to commit — and several of them say so directly. One explains that outbound they are pulled into the destination’s rhythm by excitement and novelty, while at home “there is not that level of novelty and excitement. Mostly just doing laundry.” Nobody forces you to adapt on your own sofa, so you drift back for a week or more without noticing. That is a behavioural explanation, not a measured one, and we are flagging it as our inference rather than publishing it as a finding.

The practical consequence survives either way, and it is the same conclusion from both directions: arrive a day early. Whatever the mechanism, a traveller who has a first day with nothing scheduled adapts better than one who has booked a tour for the morning after landing.

What that means for a booking, in plain numbers. On a 9-hour eastward hop (London to Los Angeles is 8 hours west; New York to London is 5 east), budget roughly one day per time zone eastbound and about two days per three zones westbound. So a 5-zone eastward flight is a ~5-day adjustment at the CDC’s average rate, and a 5-zone westward one is closer to 3.3 days. That arithmetic — not the destination’s timezone label — is what should shape how much you pack into your first two days.

It is also why the “how many zones is too many” question has a slightly unsatisfying answer. The CDC’s clinical definition of jet lag disorder requires travel across at least two time zones plus daytime impairment within one to two days of arrival, so two zones is where it formally begins. The literature’s practical threshold for intervention is higher: the Cochrane review recommends melatonin for five or more zones, especially eastward, and says 2-4 zones can use it if needed. Somewhere north of five is where the arithmetic stops being survivable on willpower alone.

The short-trip exception, which is counter-intuitive advice

For a trip of less than two days, do not adjust at all. The CDC’s guidance, adapted from the Walter Reed Army Institute of Research, is to keep your sleep, meals and activity on home-base time and ignore the local clock entirely. The reasoning is arithmetic: adapting to a new zone costs one to 1.5 hours per day, so on a trip of nearly two days you would spend almost the whole window mid-adjustment and arrive home worse than you left. For short trips you lose nothing by staying on your own schedule.

This is the single most useful and least-known piece of official jet lag guidance, and it is the opposite of what most people instinctively do.

What actually works, ranked by strength of evidence

1. Timed light exposure — strong evidence, and direction is everything. Light is the primary synchroniser of the circadian system, and when you take it matters more than how bright it is. Morning light exposure after the circadian nadir (roughly 2-4 hours before your habitual wake time) promotes a phase advance — the eastward shift. Evening light promotes a phase delay — the westward one. Concretely, per the Walter Reed guidance in the CDC tables: eastbound, get bright light in your morning and avoid light in your evening; westbound, avoid bright light in the early morning (window shade closed, dark sunglasses) and stay up until destination bedtime.

2. Melatonin — the strongest evidence of any drug, but almost entirely about timing. The Cochrane review of 10 randomised trials found that 8 of 10 showed reduced jet lag when melatonin was taken close to target destination bedtime, between 10pm and midnight, on flights crossing five or more time zones. The estimated number needed to treat is about 2. Two findings in that review contradict common practice: doses above 5mg are no more effective, and 2mg slow-release performed worse than a short-lived higher peak, implying a quick spike beats a long gentle release. The CDC’s own guidance is stricter still — 0.5-1mg is often enough to shift the clock, and high doses are actively discouraged because excess melatonin lingering at the wrong time can push you further out of alignment. If you are going to take it, take the smallest dose, timed to destination bedtime, and do not take it when your body clock thinks it is 12-5am when your own melatonin is already high.

3. Caffeine — useful, and easy to misuse. The Walter Reed protocol is specific: 200mg every four hours during daylight hours at your destination, and stop six hours before bedtime. Caffeine has roughly a five-hour half-life per the CDC, so that cutoff is not conservative. The direction flips by travel: caffeine in the morning when flying east, avoid it in the early morning when flying west.

4. Strategic sleep shifting — moderate evidence, low cost. Shifting your sleep one hour per day for two to three days before departure — later for westward, earlier for eastward — reduces how much you have to adjust on arrival. It is the cheapest item on this list and the easiest to skip.

5. Naps — bounded on purpose. After arrival, short naps of 20-30 minutes help sustain alertness. Longer naps actively fight you by reducing the sleep drive you need that night. Staying awake through the local day is what builds the pressure that lets you sleep locally at night.

6. Alcohol and sedatives — the well-meant mistake. Alcohol reduces sleep latency, which feels like it helps, but it increases sleep fragmentation, and both alcohol and caffeine cause dehydration, which worsens jet lag symptoms. The CDC specifically advises avoiding sedatives with long half-lives, and the AASM guidance it cites says antihistamines, long-acting benzodiazepines and long-acting benzodiazepine receptor agonists should be avoided because they worsen cognitive impairment and fall risk. Sleeping through the flight on a long-acting sedative is the commonest way to arrive at the wrong circadian phase and then wonder why the first day is ruined.

Exercise appears in the CDC’s daytime guidance as an alertness aid, but it sits clearly below the items above in the strength of its evidence for shifting the clock.

Two traveller claims worth testing, and one to discard

These come from traveller reports rather than clinical guidance, and are labelled by how well they are corroborated.

Business class does not appear to shorten jet lag. A long-haul flyer with lay-flat seats on both legs reports “Business class didn’t help much… it didn’t ameliorate the jet lag.” The mechanism is plausible — comfort changes how you feel, not when your suprachiasmatic nucleus resets — and it is a useful expectation-setter before anyone spends money on a lie-flat seat expecting to land adjusted. Single thread, but from a long-haul traveller whose account is otherwise specific and credible. Treat it as worth knowing rather than proven.

Age is reported repeatedly as a factor, and it matches the clinical risk list. Multiple independent accounts describe longer recoveries with age — one 67-year-old estimating two weeks, and a separate Boston–Vietnam forum thread reporting two weeks for a 73-year-old. The CDC lists individual genetic differences and other individual- and route-specific risk factors among the factors that make jet lag more severe. The clinical source names the category without quantifying it; the number in circulation is travellers’ own, not a measured one.

What to discard: the worst-routes list. Several sites rank “18 time zone” routes like LAX–Sydney as the worst. That is arithmetic dressed as research — it applies the zone count uniformly and ignores direction, route timing and individual variation, which by this page’s own account are the variables that decide the outcome. It is not cited here as evidence for anything.

The honest limits of this page

There is no single “how many time zones can you handle” number, and anyone quoting you one has invented it. The adaptation rates above are averages with real person-to-person spread; the CDC lists individual genetic differences among the risk factors for severe jet lag, which is a polite way of saying some people adapt fast and some do not.

The symptom threshold is not the same as the planning threshold. A survey cited by the CDC found 68% of international business travellers experience negative symptoms regularly — but “some tiredness for two days” and “jet lag disorder” are different claims, and only the second has a diagnostic definition.

Our traveller evidence is a 2019-2021 forum thread and it is openly dated. The most substantive source behind the return-leg finding is a Rick Steves community thread, now closed for inactivity, with posts of mixed and partly undated vintage. It is genuinely multi-voice — dozens of independent accounts — but it is not current-year data, and forum self-selection skews toward people who found the topic interesting enough to post about it. We are reporting it because the volume and consistency of the reports matter more than any single voice, not because it is strong evidence.

Two social sources were unreachable and neither is substituted. Reddit was blocked on this host across every route, and FlyerTalk returned 403s and scraper timeouts — one archived snapshot served navigation chrome with no posts in it. YouTube descriptions and transcripts resolved; comments did not load, so nothing sourced to comment threads appears here. Those are limits of our tooling, not claims that the material does not exist.

A large primary dataset exists that we could not read. A 2025 Sleep paper analysing roughly 1.5 million nights of travel-related sleep disruption would be the strongest available evidence on how long jet lag actually lasts in real travellers. Its full text sits behind a paywall we could not get past, so we are not quoting figures from it — including from abstracts and summaries that restate it. If you have institutional access, that paper is worth more than everything on this page.

The bottom line

Book your first day empty, and stop pretending the direction question is settled. On the physiological evidence, eastbound is the harder direction: about a day per time zone, versus 1.5 days per three going west. In actual traveller reports the return leg is frequently the bad one, and nobody has cleanly reconciled the two — so if you are the type to over-prepare for a short trip, the safer assumption is that the trip that costs you is the one where you come home. Beyond five zones the evidence for correctly-timed melatonin is strong enough to act on, and just as clear that more is not better.

If you take one practical thing from this page: arrive a day early. It is the single change that helps under every explanation above, and it is free.