Jet lag typically takes about one day per time zone crossed to fully resolve. Most people feel better within a few days of arriving, though recovery can stretch to a full week after longer trips. The direction you travel, your age, and how you manage light exposure all influence whether you’re on the shorter or longer end of that range.
The General Recovery Timeline
The widely cited rule of thumb is one day of recovery for each time zone you cross. Fly from New York to London (five time zones east), and you’re looking at roughly five days before your body fully adjusts. A shorter hop across two or three zones might only leave you off for a couple of days. Symptoms usually appear within a day or two of landing, peak in intensity, then gradually fade as your internal clock catches up to local time.
For most travelers, the worst of it passes within three to four days. But “feeling better” and “fully adjusted” aren’t the same thing. You might sleep reasonably well after a few nights while still noticing daytime fatigue or mild digestive weirdness for a day or two longer. If symptoms haven’t resolved or are getting worse after a week, that’s worth a conversation with a doctor.
Why Flying East Takes Longer
Your body’s internal clock doesn’t run on a precise 24-hour cycle. It naturally drifts slightly longer than 24 hours, which means it’s easier to extend your day (staying up later) than to shorten it (forcing yourself to sleep earlier). When you fly west, you’re working with that natural drift. When you fly east, you’re fighting against it.
This is why a six-hour eastward trip, like the U.S. to Europe, often feels harder than a six-hour westward trip. Eastward travel forces a “phase advance,” pushing your sleep window earlier. Your clock resists this. Westward travel does the opposite, asking you to delay sleep, which your body handles more easily. The practical difference can be an extra day or two of adjustment for the same number of time zones when heading east.
How Your Body Actually Resets
The reset process is driven by light. Specialized cells in your retinas are particularly sensitive to blue light and send signals directly to the brain’s master clock, a tiny cluster of neurons that coordinates your sleep-wake cycle, hormone release, body temperature, and digestion. When light hits these cells at a time your brain doesn’t expect, it triggers a chain of genetic activity that gradually shifts the clock forward or backward.
The key limitation is that this shift can only happen so fast. Your master clock adjusts incrementally, which is why recovery takes days rather than hours. Every organ system runs its own local clock too, and these peripheral clocks don’t all resynchronize at the same speed. Your sleep cycle might normalize before your gut does, which is why digestive symptoms sometimes linger after you’re sleeping reasonably well again.
Age and Individual Differences
Age affects jet lag in a somewhat surprising way. Research on older adults found that their circadian temperature rhythms actually shifted at a comparable speed to younger people after a six-hour time change. The clock itself adjusted fine. But sleep disruption and daytime sleepiness lasted significantly longer in older participants and showed little of the gradual improvement that younger subjects experienced over the same period. In other words, the biological clock may reset on schedule, but the ability to sleep well in the new time zone recovers more slowly with age.
Other factors that influence recovery speed include how well you slept before the trip, how many time zones you crossed, whether you’re a naturally early or late sleeper, and how much daylight you get after arrival. People who spend the first few days indoors in dim hotel rooms tend to adjust more slowly than those who get outside.
What Speeds Up Recovery
Light exposure is the single most powerful tool for resetting your clock, and timing matters more than intensity. After eastward travel, morning sunlight helps push your clock earlier. After westward travel, evening light helps delay it. Even overcast daylight is far brighter than indoor lighting and effective for this purpose, though research on workplace lighting has found that sustained exposure to bright indoor light (around 2,500 lux, comparable to being near a sunny window) can also produce meaningful circadian shifts.
A few practical strategies that consistently help:
- Follow local time immediately. Eat meals and go to bed at times appropriate for your destination, even if your body disagrees. This gives your clock consistent cues.
- Get outside during the day. Natural sunlight is the strongest signal your brain uses to recalibrate. Prioritize outdoor time in the first few days.
- Limit naps to 30 minutes. Long naps feel restorative but delay your adjustment by reducing your sleep pressure at night.
- Shift your schedule before you leave. Moving your bedtime 30 minutes earlier each night for a few days before an eastward trip (or 30 minutes later before a westward trip) can shave time off your adjustment.
Melatonin Timing and Dosage
Melatonin supplements can help, but their value depends almost entirely on when you take them. The hormone works as a timing signal, not a sedative. Taking it at the wrong time can actually shift your clock in the wrong direction.
For eastward travel, taking a low dose about 90 minutes before your target bedtime helps advance your clock, pushing it earlier. For westward travel, taking it when your body thinks it’s morning (even if it’s evening locally) can help delay the clock. The CDC notes that doses of 0.5 to 1 mg are often enough to produce a circadian shift. Higher doses above 5 mg aren’t recommended because excess melatonin lingers in your system and can end up active at the wrong time of day, undermining the shift you’re trying to create. Taking melatonin during the window when your body is already producing it naturally (roughly midnight to 5 a.m. on your internal clock) is also less effective.
What to Expect Day by Day
After crossing five or six time zones eastward, a typical recovery arc looks something like this. Day one, you’re awake at 3 a.m. and crashing by mid-afternoon. Days two and three, you’re waking early but making it closer to a normal bedtime. By day four or five, sleep timing feels roughly normal, though you might still fade in the late afternoon. Full sharpness and digestive regularity often return a day or two after sleep normalizes.
Westward trips across the same distance tend to compress this timeline by a day or so. You’ll find yourself unable to stay awake in the evening initially, then gradually pushing your natural bedtime later until it aligns with local time. The adjustment feels less jarring because you’re extending your day rather than compressing it, and most people notice they’re functioning well within three to four days.