Jet Lag Recovery Time Calculator
After crossing time zones, your circadian clock needs time to re-align with local daylight. Enter the zones crossed, direction and arrival date to estimate when you should be fully adjusted.
Please enter 0–12 zones and a valid arrival date.
Estimated recovery time
6
—
Severity
—
Expected full-recovery date
—
This is a sleep-medicine rule of thumb. Individual variation in age, fitness and trip structure changes the real rate.
Formula
Eastward: days ≈ zones × 1 · Westward: days ≈ zones ÷ 1.5
- · Days-per-zone is a sleep-medicine rule of thumb cited by Mayo Clinic, Harvard Health and AASM.
- · Eastward travel requires phase-advancing your circadian clock — the harder direction.
- · Westward travel requires phase-delaying — generally easier.
- · The arrival-date input is used only to project the expected full-recovery date (rounded up to whole days).
- · Morning daylight exposure and an earlier first-night bedtime can speed adaptation; for short trips many travellers stay on home time.
Frequently asked
Why is eastward jet lag worse than westward?
The human internal clock naturally runs slightly longer than 24 hours, so it is easier to delay (westward) than to advance (eastward). For the same number of zones, westward typically takes about two-thirds the recovery time.
How do I count how many time zones I crossed?
Take the difference between the two cities' UTC offsets. Hong Kong is UTC+8 and London is UTC+0, so 8 zones. New York is UTC−5 and Paris is UTC+1, so 6 zones. Crossing the International Date Line does not change the count — only the actual hour difference matters.
At how many zones do people start to feel jet lag?
Within 2 zones the impact is mild and usually resolves in a night or two. 3–6 zones are moderate, with a few days of disrupted sleep and daytime fatigue. 7+ zones (typical transcontinental flights) often require around a week to fully resolve.
How can I speed up adjustment?
Get plenty of natural daylight at the destination (morning for eastward, evening for westward), eat on local time, and avoid long naps on the first day. For long flights, melatonin under medical guidance and a gradual pre-trip phase-shift of bedtime can help.
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