Jet Lag Calculator
A day-by-day light and sleep plan that moves your body clock to your destination faster.
General guidance based on circadian research, not medical advice. Times are destination local time.
How the plan is built
Your body-temperature minimum — the low point of your clock — is estimated at 2.5 hours before your usual wake time. Light in the three hours after it shifts your clock earlier, light in the three hours before it shifts it later. Each day the plan moves that low point toward the destination by about 1 hour (eastward) or 1.5 hours (westward) and places the light windows around it. All calculations happen in your browser.
Rule of thumb
| Time zones crossed | Eastward | Westward |
|---|---|---|
| 3 | ≈ 3 days | ≈ 2 days |
| 5 | ≈ 5 days | ≈ 4 days |
| 7 | ≈ 7 days | ≈ 5 days |
| 9 | ≈ 9 days | ≈ 6 days |
| 11 | ≈ 11 days | ≈ 8 days |
How long does jet lag last?
Your body clock shifts by roughly one hour per day when you fly east and about one and a half hours per day when you fly west. Crossing six time zones eastward therefore takes around six days to fully adjust without help — timed light exposure can shorten that noticeably.
Why is flying east worse?
Flying east means going to bed and waking up earlier than your body wants. The human clock naturally runs slightly longer than 24 hours, so delaying it (westward) is easier than advancing it (eastward).
How does light help with jet lag?
Light is the strongest signal for the body clock. Light in the hours after your body-temperature minimum (usually 2–3 hours before you normally wake) moves the clock earlier; light in the hours before it moves the clock later. Getting the timing wrong can push the clock the wrong way.
Should I take melatonin?
Low-dose melatonin taken in the evening at your destination can help after eastward flights. Rules differ by country and it is not suitable for everyone — ask a pharmacist or doctor first.