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Jet Lag Calculator

The Jet Lag Calculator estimates how far your destination clock is ahead of or behind your home clock and turns that shift into a gradual pre-trip sleep adjustment. It is a planning aid for travelers who want to move bedtime in small steps before departure.

The suggested schedule is based on the total time-zone change, the number of preparation days, and the maximum daily shift you are comfortable making. It is not a medical prediction of symptoms, and individual responses vary with flight timing, sleep debt, light exposure, age, and health.

Travel adjustment plan

hours
hours
days
hours
Result
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Suggested daily sleep shift
Total zone change—
Shift bedtime—
Minimum days at chosen pace—
Unadjusted shift at departure—

1. Enter home and destination offsets
Use the UTC offsets in effect on the arrival date.

2. Choose preparation time
Enter how many full days you can use to adjust before departure.

3. Set a comfortable daily limit
A smaller limit creates a gentler plan but may leave part of the shift for after arrival.

4. Follow the direction
For an eastward clock advance, move bedtime earlier; for a westward clock delay, move it later.

5. Review any remaining shift
The unadjusted amount indicates how much clock change remains when the trip begins.

Shortest clock shift = Destination offset − Home offset, normalized to −12 to +12 hours Suggested daily shift = min(Maximum daily shift, |Clock shift| ÷ Preparation days) Remaining shift = |Clock shift| − Suggested daily shift × Preparation days

The sign determines direction: a positive shift generally means moving sleep earlier, and a negative shift means moving it later. The model assumes equal adjustment each preparation day.

What the result means

The main result is the amount to move your sleep schedule each preparation day.

This is a general planning estimate, not medical advice or a guarantee of symptom severity.

Given: home UTC+9, destination UTC+1, four preparation days, and a maximum shift of 1 hour per day.

Calculation: Clock shift = 1 − 9 = −8 hours. Daily shift = min(1, 8 ÷ 4) = 1 hour. Four days adjust 4 hours, leaving 4 hours.

Result: Move bedtime about 1 hour later each day; 4 hours of shift remain at departure.

Why is the shift normalized to 12 hours?

The calculator uses the shorter clock direction around a 24-hour day. Flight itinerary and arrival timing can still affect the best practical plan.

Does a positive shift always mean travel east?

Usually, but not always when crossing the International Date Line. The tool describes clock direction rather than geography.

What if I have only one preparation day?

The daily shift is capped at the maximum you enter, and the remainder is shown separately.

Can this predict how tired I will feel?

No. It estimates schedule adjustment only; fatigue and sleep disruption vary widely between people and trips.

Should I change meal times too?

Some travelers align meals and light exposure with the new schedule, but this calculator only quantifies sleep-time movement.