Jet Lag Recovery Calculator
Estimate jet lag severity and recovery time based on time zones crossed and travel direction.
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How to use this calculator
Eastward travel is harder because you lose time and must advance your body clock — each time zone adds roughly 1 full recovery day. Westward travel is easier (gaining time), so each zone adds about 0.67 days. An age multiplier adjusts for the fact that older travelers typically recover more slowly from circadian disruption.
- 1
Count the number of time zones between your departure and destination cities — this is the primary driver of jet lag severity.
- 2
Select your travel direction (eastward or westward) and your age group, as both affect recovery speed.
- 3
Review your severity rating and the recommended adaptation strategy to plan your pre- and post-flight schedule.
Frequently asked questions
How does the calculator turn time zones into recovery days?
Base days = zones crossed × 1.0 for eastward travel or × 0.67 for westward travel. That is multiplied by an age factor (0.8 under 30, 1.0 for 30 to 60, 1.3 for 60 and over) and rounded up to a whole day. Five zones east for a 30-to-60 traveller gives 5 days; five zones west gives ceil(3.35) = 4 days.
Why is the severity label based only on zones crossed?
The thresholds are fixed in the code: up to 2 zones is Mild, 3 to 4 Moderate, 5 to 6 Significant and 7 or more Severe. Direction and age change the recovery days but not the label. Six zones east for a senior shows 8 days yet is still labelled Significant.
Does the flight duration change the result?
No. The flight duration field is collected but not used in the calculation, so changing it does not alter the days or the severity. Only zones crossed, direction and age group matter.
What is the maximum number of zones?
The tool caps the input at 12, because the clock difference between two places cannot exceed 12 hours in either direction. Entering 20 gives the same answer as 12: 12 days for an eastward 30-to-60 traveller, labelled Severe. A value of 0 returns 0 days.
Is the recovery time a medical prediction?
No. It is a rule-of-thumb estimate of roughly one day per zone going east and about two-thirds of a day per zone going west, scaled by age. Individual sleep patterns, the time you land, light exposure and how tired you were before departure all change the real experience. The tool gives no medical advice; talk to a health professional about sleep, medicines or supplements.
What is the adaptation strategy line?
A short generic scheduling suggestion shown for the direction you chose: shifting bedtime earlier for eastward trips and later for westward ones, with a matching light-exposure and nap note. It is the same text for every number of zones, and it is not tailored to your itinerary or health.
How should I count time zones?
Subtract the local clock hours at your origin from the destination. If you leave London at UTC+0 and land in Dubai at UTC+4, you cross 4 zones east. Half-hour zones such as India’s UTC+5:30 can be rounded to the nearest whole number; the tool takes any non-negative number but treats it as a plain multiplier.
Jet lag recovery calculator: days per zone, direction and age
The rule behind the estimate
The calculator applies a well-known rule of thumb: about a day to adjust for each time zone crossed when travelling east, and around two-thirds of a day per zone when travelling west. In the code those become multipliers of 1.0 and 0.67. The result is multiplied by an age factor and rounded up to a whole day, then converted to hours by multiplying by 24. No other input, including flight duration, enters the sum.
| Zones crossed | Severity label | Eastward days | Westward days |
|---|---|---|---|
| 2 | Mild | 2 | 2 |
| 4 | Moderate | 4 | 3 |
| 6 | Significant | 6 | 5 |
| 8 | Severe | 8 | 6 |
Worked examples
These came from running the tool with the settings shown.
| Inputs | Recovery | Hours | Severity |
|---|---|---|---|
| 5 zones east, 30 to 60 | 5 days | 120 | Significant |
| 5 zones west, 30 to 60 | 4 days | 96 | Significant |
| 8 zones east, 60 and over | 11 days | 264 | Severe |
| 3 zones west, under 30 | 2 days | 48 | Moderate |
| 20 zones entered (capped at 12), east, 30 to 60 | 12 days | 288 | Severe |
How age shifts the number
The age multipliers are 0.8, 1.0 and 1.3. For six zones east, the under-30 group gets 5 days, the 30 to 60 group gets 6 and the 60-and-over group gets 8. Because the result is rounded up, a small change in the multiplier can add a full day. The multipliers are assumptions built into the tool, not values taken from a clinical study, so use them as a way to rank scenarios, not to predict your own recovery.
Why west and east differ
The tool treats flying east as harder, because the body clock has to be pulled earlier, and flying west as easier. This is why a 4-zone trip east shows 4 days, while the same trip west shows 3. The tool does not model overnight arrival times, stopovers, shift work or pre-trip schedule changes, all of which affect how long adjustment takes in practice.
Using the output for planning
Treat the recovery days as a planning buffer. If the tool shows 6 days for an eastward trip, avoid scheduling an important presentation on the first two or three days after landing. A short trip to a distant zone may be over before you adapt, so compare the recovery days with your trip length and consider whether staying on home time is easier. For symptoms or sleep problems, consult a clinician. If you often cross the same number of zones, run the tool for both directions and both age groups you care about, and keep the table of days for future trips.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →