Jet lag calculator
Pick your departure and arrival cities. The calculator estimates how many days you’ll be off, the direction of the shift, when to seek bright light, and a three-day pre-trip schedule to halve recovery time.
Crossing 9 timezones going east. Phase advance — the harder direction.
Rough estimate based on ~1 day per timezone east, ~⅔ day per timezone west.
Destination is ahead of departure by 9h.
Light strategy on arrival
Light is the strongest zeitgeber — it tells your circadian clock what time it is.
Bright light 6:00–10:00 AM destination time
Avoid bright light 8:00–11:00 PM destination time
Pre-trip schedule shift
Start shifting bedtime three days before. By the time you fly, you’re halfway adjusted.
- 3 days beforeBedtime 1h earlier
- 2 days beforeBedtime 2h earlier
- 1 day beforeBedtime 3h earlier
The three levers that actually move jet lag
Light exposure is the strongest. Light at the right time of day in the destination timezone tells your circadian clock that now is morning (or evening). Get it wrong and you can shift the wrong way. Mornings for eastward travel; evenings for westward.
Pre-trip shifting is the easiest lever to pull but the one most travelers skip. Moving your bedtime by an hour a day for three days before the flight gets you halfway adjusted before you even take off.
Melatonin (low dose, correct timing) works as a circadian signal, not a sleep aid. 0.5 mg, 4–6 hours before target bedtime, starting 2 days before departure. High doses (3–10 mg) are common in stores but the evidence supports much lower doses for jet lag specifically.
What the recovery estimate is based on
For most healthy adults, the body shifts about 1 hour per day eastward (phase advance) and 1.5 hours per day westward (phase delay). Crossing 6 timezones east is roughly a 6-day recovery; crossing 6 timezones west is roughly 4 days. Above 9 timezones, the body actually adjusts the “other way” — it’s shorter to go the opposite direction around the clock — and the calculator accounts for that. The phase-shift rates are from Sack et al., 2007, the AASM's circadian rhythm sleep disorders review.
If you only do one thing
Step outside in bright daylight for 20 minutes within an hour of waking on day 1 in the destination. That single intervention is the highest-leverage action you can take and costs nothing.
Frequently asked questions
How long does jet lag last?
Rule of thumb: about 1 day per timezone crossed going east, and 2/3 day per timezone going west. A flight from New York to London (5h east) takes about 5 days to fully adjust; the same flight in reverse takes about 3–4 days. The pre-trip schedule shift and light-timing strategy below can cut recovery roughly in half.
Why is flying east harder than flying west?
Your internal clock naturally runs slightly longer than 24 hours (about 24.2 in most people). Flying west means staying up later — phase delay — which is what your body wants to do anyway. Flying east forces phase advance, going to bed earlier than your clock thinks it should, which is harder.
Should I take melatonin for jet lag?
Yes, with timing. Melatonin shifts the circadian clock when taken 4–6 hours before your target bedtime in the new timezone, starting 2–3 days before the flight. The dose that has the most evidence is 0.5 mg (lower than the 5–10 mg most supplements sell). Taking high doses at the wrong time can shift you the wrong way.
What about the Argonne anti-jet-lag diet?
The 4-day feast/fast protocol has weak evidence — it’s been around since the 1980s but hasn’t consistently outperformed simpler interventions in modern studies. Light timing has much stronger evidence and is the foundation of every modern protocol.
How do I avoid jet lag entirely?
For short trips (under 3 days), don’t try to adjust — keep your home schedule. For longer trips, start shifting bedtime 3 days before departure, use bright morning light (or a 10,000-lux lamp) in the destination direction, and consider 0.5 mg melatonin 4–6 hours before target bedtime starting 2 days before.
Does this calculator handle daylight saving?
It uses standard UTC offsets and doesn’t auto-adjust for DST. If you’re traveling around a DST transition, double-check the offset for your travel dates — a 1-hour error in the calculator means a 1-hour error in your light strategy.