Jet lag is usually worse flying east because it forces your body clock to run earlier, and most people's internal clock finds it much easier to shift later. As a rough guide, expect about one day per time zone going east, and noticeably less going west.
Free toolJet Lag CalculatorDays to adjust, plus a shift-before-you-fly schedule.Your body clock runs a little long
Deep in your brain sits a master clock that times sleepiness, alertness, body temperature and hormones across the day. Left completely on its own, without daylight or alarms, it doesn't run exactly 24 hours.
In a carefully controlled Harvard study, the average intrinsic period of the human body clock came out at about 24.18 hours. That's only 11 minutes longer than a day, but it matters. Every morning, daylight nudges your clock a little earlier to keep it lined up with the 24-hour world.
Because your clock naturally drifts late, pushing it later is going with the grain. Pushing it earlier is going against it.
What that means when you fly
- Flying west (say, New York to Los Angeles): the local clock is behind yours. You need to stay up later and sleep in later. Your body clock is happy to stretch, so this tends to go fairly smoothly.
- Flying east (say, New York to London): the local clock is ahead. You need to fall asleep earlier and wake earlier, while your body is still saying it's early evening. That's the direction the clock resists.
It's the same reason most people find it easier to stay up an hour late on a Saturday than to go to bed an hour early on a Sunday. Eastward travel is that Sunday night problem, multiplied by several hours.
How long each direction takes to recover
The figures below use a common rule of thumb, the same one behind our jet lag calculator: about one day per time zone going east, and the body clock moving roughly 1.5 hours a day going west, rounded up.
| Time zones crossed | Flying east | Flying west |
|---|---|---|
| 1 | 1 day | 1 day |
| 2 | 2 days | 2 days |
| 3 | 3 days | 2 days |
| 4 | 4 days | 3 days |
| 5 | 5 days | 4 days |
| 6 | 6 days | 4 days |
| 7 | 7 days | 5 days |
| 8 | 8 days | 6 days |
| 9 | 9 days | 6 days |
| 10 | 10 days | 7 days |
Treat these as ballpark numbers. Real recovery depends on how much daylight you get, how well you slept before the trip, your age, and whether you're naturally a morning or evening type. You may feel mostly normal a day or two before the estimate runs out.
Beyond about 10 to 12 time zones, direction starts to matter less, because the clock may adjust by going the "short way" around. We cover that in jet lag from the US to Asia.
What eastward jet lag feels like
Because you're asking your body to sleep before it's ready, eastward jet lag tends to show up as:
- Lying awake for hours at local bedtime
- Feeling groggy and heavy in the morning, sometimes until lunch
- An afternoon crash when your home clock says it's the middle of the night
Westward jet lag is more often the opposite: fading hard in the early evening and waking at 4 or 5 AM.
How to make eastward trips easier
- Start shifting before you fly. Go to bed and get up an hour earlier each day for up to three days before an eastward trip. Research on pre-flight schedules found that one hour a day, paired with morning light, moved the body clock without leaving people misaligned.
- Get daylight at the right time. After flying east, light in the morning helps pull your clock earlier. Keep evenings dim. After a big eastward jump (6 or more hours), very early light can push you the wrong way for the first day or two, so late-morning light is a safer bet.
- Keep naps short. If you're wiped out on arrival day, a 20-minute nap before mid-afternoon is fine. A long nap makes the first night harder. The nap calculator helps you time one.
- Go easy on caffeine after lunch. It's tempting to power through with coffee, but a late cup makes that first early bedtime even harder.
- Ask about melatonin before you rely on it. Melatonin is widely used for jet lag, but the right dose and timing depend on your trip and your health. Check with a pharmacist or doctor first, especially if you take other medications.
For a worked example with real times, see our New York to Europe plan.
Why westward trips still aren't free
West is easier, not effortless. You'll still have a few days of waking too early, and long westward flights come with their own travel fatigue from dry cabin air, cramped seats and broken sleep. Anchor your schedule by staying up until at least 9 or 10 PM local time and getting daylight in the late afternoon.