Jet Lag Planner

Lark or Owl? How Your Chronotype Shapes Your Jet Lag

Are you the one up and cheerful at 6am, or the one who only really switches on somewhere around midnight? That early-or-late wiring is your chronotype, and it colours how jet lag treats you. It nudges your body clock's lowest point, and with it the best time to grab daylight or hide from it, a touch earlier if you're a morning lark and a touch later if you're a night owl. Before you go rebuilding your whole plan around it, though, the effect is genuinely modest, somewhere around half an hour, so it fine-tunes your plan more than it rewrites it. The short of it is that larks tend to cope a little better flying east, and owls a little better flying west.

What a chronotype actually is

Morning types wake early and run out of steam early; evening types do the whole thing in reverse. It's about half genetic, which surprises most people the first time they hear it: a Finnish study of 8,753 adult twin pairs put the heritability at 49.7 percent, with the rest down to environment. It also drifts across your life, running later through the teenage years and then creeping earlier again as you get older. And the easiest way to place yourself is to picture a lazy holiday with no alarm and nothing to be up for, then ask when you'd naturally drop off and wake. Reliably early makes you a lark, reliably late an owl, and if the honest answer is "somewhere in the middle, depends on the day," then congratulations, you're in the majority.

Where it grabs your clock

Your body clock pivots on its temperature low point (the temperature minimum, if you want the textbook term), the sleepy trough that lands a few hours before you'd naturally wake: about three, as a clinical rule of thumb, or two to four by the CDC's wider estimate. Catch bright light after that trough and your clock shifts earlier; catch it before, and it shifts later. Time it backwards and you'll cheerfully shunt yourself the wrong way, which is the one mistake worth avoiding. The full mechanics live in Your Body Clock: Circadian Rhythm and the Temperature Minimum if you want them.

Your own wake time already tells you most of what you need to know. A lark who's up at 5:30 has that low point somewhere near 2:30am; an owl who surfaces at 9:00 has one closer to 6. In one tightly controlled lab study of 10 morning types and 12 evening types, the owls ran their temperature and melatonin rhythms about two to three hours behind the larks, but that figure is the distance between the two extremes. Once you've allowed for the plain fact that owls wake later anyway, the leftover nudge that chronotype adds for an ordinary person is small, about that same half hour.

How that changes your plan, a little

In practice it's a small adjustment you can do in your head. Start by estimating your low point at about three hours before your normal wake time, then shuffle that guess about half an hour earlier if you're a clear lark or half an hour later if you're a clear owl, and slide your get-light and avoid-light windows along by the very same amount. That's the entire manoeuvre. A lark chasing an eastward shift starts the morning light a fraction sooner; an owl delaying for a westward trip drags the evening light a fraction later. All of it sits on top of the real plan, which is still set by the direction you're flying and how many time zones you're crossing, not by whether you happen to like mornings.

And no, you can't reprogram yourself into a lark the week before a big trip. You can nudge your timing with light and schedule, which is exactly what pre-trip adjusting does, but the underlying type is roughly half genetic and won't flip, so you're far better off working with it than trying to overrule it. If you've got a few days to play with before you fly, Adjusting Before You Fly: How Many Days You Really Need shows what that nudge realistically buys you.

Larks fly east, owls fly west

Flying east asks you to advance: earlier nights, earlier mornings. Larks already live there, so they start half a step nearer destination time before they've lifted a finger. Flying west asks for the opposite, later nights and later mornings, which is precisely where an owl naturally drifts. Line those two facts up and you get the neat little rule of thumb, that larks have the easier ride going east and owls the easier ride going west.

For all that, most people find the eastward leg the harder one whatever their type, since the clock re-adjusts about half again as fast heading west, so don't count on your chronotype to rescue you from it. If you're an owl flying east, brace for the classic combination of lying wired at bedtime and feeling wrecked in the morning, and lean hard on early daylight to haul yourself round. If you're a lark flying west, expect to ping awake at dawn instead, and lean on evening light to hold yourself back. Which light, and when, is really the heart of the whole business, and Morning Light or Evening Light: Which Way You Shift Your Clock is the piece that spells it out. There's more on why east flattens everyone in Why Flying East Is Harder Than Flying West.

Fun fact

Teenagers turn into temporary owls, and it's pure biology rather than teenage bloody-mindedness. Somewhere around puberty the body clock starts drifting later, bottoms out in the late teens, and then slowly winds back earlier for the rest of your life. It's why a fifteen-year-old is wide awake and texting at 11pm while their grandparent has been up and pottering since five, and it's a big part of why later school start times keep landing back on the agenda.

How the Jet Lag Planner handles this

Tell the Jet Lag Planner whether you run early, late, or somewhere in between, and it nudges your estimated low point and your light windows by that modest amount without ever pretending your chronotype rewrites the whole plan. If you aren't sure which one you are, the average setting is close enough for almost everyone, so don't lose sleep over it. Build a plan, flip the chronotype setting back and forth, and watch how little (or, now and then, how much) your timing actually moves.

Sources

General wellness information, not medical advice. Talk to a clinician before changing your schedule if you have a sleep or health condition.

Last reviewed August 5, 2026.

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General wellness information, not medical advice. Talk to a clinician before changing your schedule if you have a sleep or health condition. © 2026 XOR Limited.