You've just landed after a long-haul flight, and your body has no idea what time it is. You're exhausted at noon and wide awake at 3am. The question everyone asks: how long will this last?
The answer depends on several factors — how many time zones you crossed, which direction you flew, your age, and what you do in the first 48 hours after arrival. Our jet lag calculator below gives you a personalized estimate, but first, let's understand the science behind the numbers.
How Jet Lag Recovery Time Is Calculated
Jet lag occurs when your internal body clock — your circadian rhythm — is out of sync with the local time at your destination. Your body's master clock, located in the suprachiasmatic nucleus (SCN) of the brain, can only shift by about 1-1.5 hours per day naturally.
This biological limit is the basis for every jet lag recovery estimate. The more time zones you cross, the more days your body needs to realign its roughly 24.2-hour internal cycle with the new local time.
The Basic Formula
Sleep researchers use a straightforward calculation as a starting point:
Estimated Recovery Days = Time Zones Crossed × 0.7
This means crossing 6 time zones gives you a baseline of about 4.2 days of jet lag. But this is just the starting point — several factors push that number up or down.
Direction Matters: East vs. West
Traveling eastward is significantly harder on your body than westward. Here's why: your circadian rhythm naturally runs slightly longer than 24 hours (about 24.2 hours on average). This means your body finds it easier to delay sleep — staying up later, as you'd need when flying west — than to advance sleep, which is what eastward travel demands.
Studies show that eastward recovery takes roughly 50% longer than westward recovery across the same number of time zones. Our calculator adds approximately one extra recovery day for eastward flights.
Age and Sleep Quality
Two more factors significantly affect your recovery:
- Age: Travelers over 50 typically need an additional day to recover compared to younger adults. The circadian system becomes less flexible with age, making it harder for the body clock to shift.
- Sleep on the flight: If you managed to sleep during the flight (ideally during nighttime at your destination), your body has already started adjusting, which can shave a day off recovery.
Try the Jet Lag Calculator
Enter your flight details below to get a personalized recovery estimate with specific tips for your route.
Use our full calculator with timezone selection and personalized tips:
Open Jet Lag Calculator →Jet Lag Recovery Times for Common Routes
Here's a quick reference table for popular international routes. These assume an adult aged 31-50 who didn't sleep much on the flight:
| Route | Zones Crossed | Direction | Est. Recovery |
|---|---|---|---|
| New York → London | 5 | East | 5-6 days |
| London → New York | 5 | West | 3-4 days |
| Los Angeles → Tokyo | 8 (via date line) | West | 5-6 days |
| Tokyo → Los Angeles | 8 (via date line) | East | 7-8 days |
| Dubai → Singapore | 4 | East | 3-4 days |
| London → Sydney | 11 | East | 8-10 days |
| New York → Paris | 6 | East | 5-7 days |
| Chicago → London | 6 | East | 5-6 days |
Keep in mind these are estimates for unassisted recovery. Using strategic light exposure, melatonin timing, and the techniques below can cut recovery time by 30-50%.
5 Evidence-Based Ways to Speed Up Recovery
Once you know your expected recovery time, here's how to shorten it:
1. Strategic Light Exposure
Light is the most powerful signal for resetting your circadian rhythm. The timing depends on your travel direction:
- Flew east? Get bright morning light for 30-45 minutes right after waking. Avoid evening light.
- Flew west? Seek afternoon and early evening light (4-7pm local time). Wear sunglasses in the morning.
Natural sunlight is far more effective than indoor lighting — even a cloudy day provides 10,000+ lux compared to about 500 lux indoors.
2. Timed Melatonin
Low-dose melatonin (0.5-1mg) taken 30 minutes before your target bedtime at the destination can significantly help. Research consistently shows it's most effective when crossing 5 or more time zones. The key insight: timing matters far more than dose. More is not better.
3. Meal Timing
Your digestive system has its own circadian clock. Eating meals at local times — even if you're not hungry — sends a powerful resynchronization signal. Eat breakfast at the local breakfast time on your first morning.
4. Strategic Caffeine Use
Caffeine can help you stay alert during your destination's daytime, but be strict about cutoff times. Stop all caffeine by noon local time for severe jet lag, or 2pm for milder cases. Caffeine's half-life of 5-6 hours means an afternoon coffee can easily sabotage your sleep that night.
5. Morning Exercise
Light exercise — a 20-30 minute walk is ideal — in the morning sunlight hits two recovery strategies at once. The physical activity promotes sleep pressure for the coming night, while the outdoor light exposure helps reset your clock. Avoid intense exercise close to bedtime.
When to Be Concerned About Jet Lag
Normal jet lag should improve steadily each day. If you're still experiencing significant symptoms after 2 weeks, or if jet lag is severely impacting your work or daily life, it's worth speaking with a healthcare provider. Persistent circadian disruption can sometimes unmask underlying sleep disorders.
Frequent travelers and flight crews face cumulative effects from repeated circadian disruption, which research has linked to increased health risks. If you fly long-haul more than once a month, proactive circadian management becomes especially important.
Get a Day-by-Day Recovery Plan
Our free WellRest iOS app creates a personalized recovery schedule based on your exact flight, with timed reminders for light exposure, melatonin, meals, and more.
Download WellRest Free →Frequently Asked Questions
How many days does jet lag last per time zone?
The general rule is about 0.5 to 1 day per time zone crossed for full recovery. Research suggests approximately 0.7 days per zone as an average, with eastward travel taking longer than westward travel for the same number of zones.
Is there a formula for calculating jet lag?
Yes. A reliable formula is: Recovery Days = (Time Zones Crossed × 0.7) + Direction Modifier + Age Modifier. Add 1 day for eastward travel and 1 day for ages over 50. Subtract 1 day if you slept well on the flight. Our calculator applies this automatically.
How long does jet lag last from the US to Europe?
Flying from the US East Coast to Europe crosses about 5-6 time zones eastward, which typically causes jet lag lasting 4-6 days. From the US West Coast to Europe (8-9 zones east), recovery can take 6-8 days without active intervention strategies.
Can you recover from jet lag in one day?
For short-haul flights crossing 1-2 time zones, yes — most people recover within a day. For longer flights crossing 5+ zones, strategic use of light exposure, melatonin timing, and meal scheduling can significantly speed up recovery but rarely reduce it to just one day.