Based on Circadian Science · East vs West · Recovery Timeline
Jet Lag Calculator —
How Long to Recover & Reset Your Body Clock
Cross multiple time zones and your internal clock falls out of sync with local time. Enter your travel details below to find out how long recovery takes and get personalized evidence-based strategies to reset faster.
Example: NYC → London = 5 hrs · NYC → Tokyo = 14 hrs
Jet lag typically lasts approximately 1 day per time zone crossed when flying east, and slightly less when flying west. A transatlantic flight from New York to London (5 time zones east) usually takes 5–7 days to fully adjust. The same flight in reverse takes 4–5 days.
Severity depends on the number of time zones crossed, direction (east is harder), your age (older adults adjust more slowly), your chronotype, and whether you use jet lag countermeasures like timed light exposure and melatonin.
Symptoms — fatigue, difficulty sleeping at the local time, reduced concentration, digestive disruption — occur because your circadian clock is anchored to your home time zone while local cues (light, temperature, meal times) push toward the new zone. Recovery happens as these signals gradually realign your clock.
Quick Reference
Jet Lag Recovery by Time Zone Difference
Days to adjust, from the measured figures in Ruscitto & Ogden (2019). Rows at 3, 6, 9 hours are the reported values; the rest are interpolated between them and marked, and past 9 hours the study reports nothing, so those are floors rather than figures.
| Shift | Example route | East — partial | East — full | West — partial | West — full | Basis |
|---|---|---|---|---|---|---|
| 1 hour | London → Paris | 1 | 1 | 1 | 1 | interpolated |
| 2 hours | London → Cairo | 1 | 3 | 1 | 3 | interpolated |
| 3 hours | London → Moscow | 1 | 4 | 1 | 4 | measured |
| 4 hours | London → Dubai | 2 | 5 | 1 | 5 | interpolated |
| 5 hours | New York → London | 2 | 5 | 2 | 5 | interpolated |
| 6 hours | Los Angeles → London | 3 | 6 | 2 | 6 | measured |
| 7 hours | New York → Berlin | 4 | 7 | 2 | 6 | interpolated |
| 8 hours | New York → Dubai | 4 | 7 | 3 | 7 | interpolated |
| 9 hours | New York → Delhi | 5 | 8 | 3 | 7 | measured |
| 10 hours | New York → Bangkok | 5+ | 8+ | 3+ | 7+ | Not measured |
| 11 hours | New York → Tokyo | 5+ | 8+ | 3+ | 7+ | Not measured |
| 12 hours | Los Angeles → Tokyo | 5+ | 8+ | 3+ | 7+ | Not measured |
Individual variation is large; age, chronotype and sleep quality all move these numbers. Highlighted rows are eastward shifts of 8 hours or more, where field studies have seen the clock re-entrain the wrong way — by delay rather than advance — which can make a long eastward trip behave like a westward one. Shifting your schedule earlier for a few days before departure reduces that risk.
The part that actually moves your clock
When to get light, and when to avoid it
“Get morning light flying east” is the advice everyone repeats, and it is the advice that fails on long trips. Light does not shift your clock by the destination’s time — it shifts it relative to CBTmin, which travels with your body.
| Direction | What you want | Seek light | Avoid light |
|---|---|---|---|
| Flying east | Phase advance — body clock earlier | Light in the 12 hours AFTER your CBTmin, strongest 3–6 hours after it | Light in the 12 hours BEFORE your CBTmin |
| Flying west | Phase delay — body clock later | Light in the 12 hours BEFORE your CBTmin, strongest 3–6 hours before it | Light in the 12 hours AFTER your CBTmin |
CBTmin — your core body temperature minimum — is the pivot. It falls roughly 4 hours after your habitual bedtime, so for an 11pm sleeper it is around 3am. It moves with your body, not with the local clock, which is why it drifts a little earlier or later each day as you adjust.
Flying east: On day one that means light from roughly your body’s 3am to 3pm, not the destination’s. Because CBTmin shifts earlier as you adapt, the useful window walks earlier each day too.
Flying west: On day one that means light from roughly your body’s 3pm to 3am. This is the easier direction: the human circadian period runs slightly longer than 24 hours, so the clock delays more willingly than it advances.
This is why a long eastward trip can go wrong. Destination morning light can land before your CBTmin rather than after it, which delays the clock instead of advancing it — the body takes the long way round. That is the antidromic re-entrainment flagged in the table above.
Melatonin timing is not the same as melatonin for sleep
Ruscitto & Ogden report that a 3.0 mg dose produces more reliable phase shifts than 0.5 mg. Larger is not better for sleepiness, and the two uses have different optimal timings.
East: For maximum phase advance: about 11.5 hours before CBTmin, which is roughly 6.5 hours before habitual bedtime — near 4:30pm for an 11pm sleeper.
West: For maximum phase delay: about 4 hours after CBTmin, which is roughly 1 hour after habitual wake — near 8am for a 7am riser.
This is general information, not medical advice. Melatonin is a prescription medicine in some countries and an unregulated supplement in others, doses on the label are often far higher than those studied, and it interacts with several common medications. Talk to a clinician or pharmacist before using it, particularly if you are pregnant, taking anticoagulants or anticonvulsants, or treating a child.
Sources
- Ruscitto C, Ogden J. Interventions to Minimize Jet Lag After Westward and Eastward Flight. Frontiers in Physiology, 2019
Day counts to partial and complete adjustment, the phase response curve windows, and the melatonin timings quoted above.
- American Academy of Sleep Medicine — Clinical Practice Guideline for the Treatment of Intrinsic Circadian Rhythm Sleep-Wake Disorders
Clinical context for timed light exposure and melatonin.
General information, not medical advice. Persistent sleep problems after travel, or shift-work sleep difficulties that do not resolve, are worth raising with a clinician.
Circadian Science
Why Traveling East Is Harder Than West
Flying East — Phase Advance
When you fly east, local time is ahead of your body clock. If your body thinks it is 10 PM, local clocks say 3 AM. You need to go to sleep before your body is ready and wake before your body clock expects morning.
This is called a phase advance — your clock needs to move earlier. The human circadian clock naturally runs at slightly longer than 24 hours (approximately 24.2 hours), making it biologically easier to stay up later (delay) than to go to sleep earlier (advance).
- Symptoms: insomnia at local night, extreme morning fatigue
- Key fix: seek bright morning light at destination
- Avoid: evening light at destination (it delays further)
- Melatonin: take in early evening at destination
Flying West — Phase Delay
When you fly west, local time is behind your body clock. Your body wants to sleep when local time is still evening. You feel sleepy at dinner time but cannot sleep in the next morning because your body clock wakes you early.
This is a phase delay — your clock needs to move later. Since the human clock naturally tends later than 24 hours, this aligns with our biology. Recovery is typically 20–30% faster than equivalent eastward travel.
- Symptoms: early-morning waking, daytime sleepiness at dinner
- Key fix: seek evening light at destination
- Avoid: morning light (it advances your clock further)
- Melatonin: optional — less critical than for eastward travel
Evidence-Based Strategies
8 Tips to Beat Jet Lag Faster
Supplement Guide
Melatonin Timing for Jet Lag
Melatonin is most effective when taken at the correct local time — not at home-time bedtime. Here is how to use it for each travel direction.
Flying East
- Take 0.5–3mg at destination bedtime (e.g., 10 PM local)
- Continue for 3–5 nights until adjusted
- Do not take at home-time bedtime (wrong signal)
- Combine with morning bright light for best effect
Flying West
- Melatonin is optional but helpful for initial nights
- Take at destination bedtime if struggling to fall asleep
- Evening light exposure is the primary strategy
- Phase delay makes westward adjustment naturally easier
Melatonin is generally considered safe for short-term use. Consult a healthcare provider before use if pregnant, nursing, or on blood-thinning medications.
Common Questions
Jet Lag Calculator FAQ
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