Circadian Jet Lag Adjustment Calculator
How many days to adjust, and when to seek light.
Enter your values
Enter the time zones crossed you are working with.
Choose one of: Eastward (Europe/Asia), Westward (Americas).
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Days to fully adjust
- 9.1 days
- Adjustment speed
- 40 min per day
- Seek bright light
- Early morning at your destination
- Avoid light
- Late evening
Quick answer
The body clock shifts about one hour per day westward and 40 minutes per day eastward, so eastward travel takes longer to adjust to.
At a glance
| What it does | How many days to adjust, and when to seek light. |
|---|---|
| Category | Health |
| Inputs needed | Time zones crossed, Direction |
| Main output | Days to fully adjust |
| Cost | Free — no sign-up, no download |
How to use the Circadian Jet Lag Adjustment Calculator
- 1Enter how many time zones you are crossing.
- 2Choose the direction of travel.
- 3Follow the light exposure guidance.
Inputs explained
- Time zones crossed
- Enter the time zones crossed you are working with.
- Direction
- Choose one of: Eastward (Europe/Asia), Westward (Americas).
Worked example
Using the values the calculator loads with:
Inputs
- Time zones crossed6
- DirectionEastward (Europe/Asia)
Results
- Days to fully adjust9.1 days
- Adjustment speed40 min per day
- Seek bright lightEarly morning at your destination
- Avoid lightLate evening
Frequently asked questions
Why is eastward harder?
The natural human circadian period is slightly longer than 24 hours, so delaying (westward) is easier than advancing (eastward).
Does melatonin help?
Low doses timed to the destination evening can speed eastward adjustment; discuss timing with a clinician.
What do I need to enter into the Circadian Jet Lag Adjustment Calculator?
Just 2 values: time zones crossed, direction. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Circadian Jet Lag Adjustment Calculator work out the answer?
The body clock shifts about one hour per day westward and 40 minutes per day eastward, so eastward travel takes longer to adjust to. The working is shown step by step so you can verify the result by hand.
Is the Circadian Jet Lag Adjustment Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.