Last updated: October 2026
How long does jet lag last?
Jet lag is your internal clock disagreeing with the wall clock. The rule of thumb researchers use: the body shifts roughly one time zone per day when the shift is eastward (clock moves forward), and a bit faster — up to about 1.5 zones per day — when the shift is westward. This calculator uses 1 day per zone eastward and 0.75 days per zone westward, rounded up, which lands in the middle of the published ranges.
| Time zones crossed | Eastward recovery | Westward recovery |
|---|---|---|
| 3 | 3 days | 3 days |
| 5 (e.g. NYC → London) | 5 days | 4 days |
| 8 (e.g. NYC → Tokyo) | 8 days | 6 days |
| 10+ | 10–12 days | 8–9 days |
These are full-adjustment estimates — you will feel noticeably better well before the last day. Most people report the worst symptoms (broken sleep, afternoon crashes, foggy mornings) in the first 2–3 days, then a long tail of slightly-off sleep.
Why flying east feels worse than flying west
Think of it this way: after a westward flight, your body wants to stay up later — and the new timezone is asking exactly that. After an eastward flight, your body wants to stay up later but the new timezone demands sleep earlier. One direction cooperates with your clock; the other argues with it. That is also why the pre-travel shift matters more for eastward trips: every hour you pre-shift is an hour you don't have to force later.
There is a second, subtler reason. The human circadian system responds to light on a curve: light in the hours before your deepest sleep pushes the clock later, light after it pulls the clock earlier. Get the timing wrong — bright light at the wrong end of the day — and you can accidentally shift your clock the wrong way, adding days to recovery. That is why the calculator gives you concrete seek/avoid windows instead of generic "get sunlight" advice.
Worked example: New York → London
New York is UTC−5, London is UTC+0: a 5-hour difference, and the shorter way around is eastward. So: 5 time zones eastward × 1 day = 5 recovery days, moderate severity. Say you fly on a Friday and normally sleep 11:00 PM–7:00 AM. The pre-travel plan moves everything earlier by one hour per day:
| Date | Bedtime | Wake time |
|---|---|---|
| Tuesday | 10:00 PM | 6:00 AM |
| Wednesday | 9:00 PM | 5:00 AM |
| Thursday | 8:00 PM | 4:00 AM |
| Friday (fly) | On the plane, behave as if it is London time | |
After landing: seek bright light 7:00–10:00 AM local (your usual wake window, now on London time) and avoid bright light 8:00–11:00 PM local. Sleep at 11:00 PM London time on arrival night — if you land exhausted, one 20-minute nap before 3 PM, alarm set. By Wednesday (travel day + 5), you should feel fully adjusted. Run your own route through the calculator above for the same treatment with your cities and schedule.
The 3-day pre-travel sleep shift
This is the highest-leverage jet lag tactic that exists, and most travelers skip it. One hour per day is small enough that your body actually follows it — bigger jumps just create pre-trip insomnia. Three days buys you 3 hours of adjustment before you even board, which can cut a 5-day recovery nearly in half. Shift meals by the same hour too; your gut has a clock as well, and eating on the new schedule reinforces the shift. If 3 days feels like a lot, even 2 days (2 hours) measurably helps.
One honest caveat: shifting earlier (for eastward trips) is genuinely unpleasant — falling asleep at 8 PM when your body says 11 PM is hard. Dim the house lights an hour before the target bedtime, keep the bedroom cool and dark, and avoid caffeine after midday on shift days. The discomfort is the point: it means the shift is working.
Light exposure rules that actually reset your clock
| Direction | Seek bright light | Avoid bright light |
|---|---|---|
| Eastward | Morning — first 3 hours after waking | Evening — last 3 hours before bed |
| Westward | Evening — last 3 hours before bed | Morning — first 3 hours after waking |
Light is the strongest time-giver your brain has — stronger than meals, exercise, or willpower. Morning light tells an eastward-shifted clock "this is the new morning, lock it in"; evening light would tell it "actually it's still daytime," undoing the shift. Outdoors on even a cloudy day delivers far more light than indoor lighting, so a 20–30 minute walk beats sitting by a window. Sunglasses count as light avoidance — wear them on the "avoid" side of the schedule if you must be outside.
Your arrival-day playbook
Arrival day sets the trajectory for the whole recovery. The travelers who adjust fastest do three things: they eat at local mealtimes even if they aren't hungry, they get outside in the correct light window, and they protect one anchor — a fixed wake time every morning, even on weekends of the trip. The wake anchor matters more than bedtime: a consistent wake time drags the rest of the rhythm into place within days.
What not to do: don't "rest up" with a 3-hour afternoon nap (it will steal your nighttime sleep and add days), don't load up on caffeine after midday local time, and don't plan anything important for the morning of day 1 after an eastward flight — that is when the fog is thickest. Schedule demanding meetings for afternoons on eastward trips and mornings on westward ones, when your old clock is still helping.
The complete jet lag recovery guide
Before you book. If you have a choice, pick flights that land in the early evening local time: you can go straight to a normal bedtime, which is the single easiest first night. Eastward red-eyes that land at 7 AM are the classic jet lag trap — you arrive destroyed, nap all day, and wake at midnight. For trips under 2 days, some frequent flyers deliberately stay on home time; the math only favors adjusting if you'll be there longer than the recovery takes.
On the plane. Set your watch to destination time at boarding and commit. If it's nighttime at your destination, create night: eye mask, earplugs, no screens, try to sleep. If it's daytime there, stay awake and stay lit — keep the reading light on, watch a film, walk the aisle. Drink water steadily; cabin air dehydrates you, and dehydration amplifies every jet lag symptom. Eat the meal that matches destination mealtime, and skip alcohol — it fragments sleep exactly when you need it whole.
The first week. Anchor a fixed wake time and defend it — this is the highest-value habit of the recovery. Exercise helps, timed like light: morning workouts after eastward flights, evening workouts after westward ones. Keep caffeine to the first half of your local day. And be patient with the tail: feeling 90% normal on day 3 of a 5-day recovery is expected, not a sign the plan failed. The last 10% — slightly early waking or a 4 PM dip — fades on its own if you hold the schedule.