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Jet Lag Calculator — Recovery Time & Light Exposure Schedule

Estimate recovery time and get a personalized adjustment schedule

Recovery Time

9 days

Severity

Moderate

Seek Light

07:00

Melatonin

20:00

Recovery Time

9 days

Severity

Moderate

Seek Light At

07:00

Melatonin At

20:00

Adjustment Rate1.0h / day
Avoid Bright Light Until06:00

Frequently Asked Questions

Q

How long does jet lag last?

Jet lag recovery takes roughly 1 day per time zone crossed when traveling westward, and 1.5 days per zone when traveling eastward. A 6-zone eastward trip (e.g., New York to Paris) takes about 9 days for full recovery. Most symptoms peak on days 2–3 and gradually improve from there.

  • Westward: ~1 day per zone crossed (6 zones = ~6 days)
  • Eastward: ~1.5 days per zone crossed (6 zones = ~9 days)
  • Symptoms peak on days 2–3 after arrival
  • Mild jet lag (1–3 zones): 1–3 days recovery
  • Severe jet lag (8–12 zones): 8–18 days full recovery
Zones CrossedWestward RecoveryEastward RecoverySeverity
1–3 zones1–3 days2–5 daysMild
4–7 zones4–7 days6–11 daysModerate
8–12 zones8–12 days12–18 daysSevere
Q

Why is jet lag worse flying east?

The human circadian clock naturally runs slightly longer than 24 hours (about 24.2 hours). Traveling east shortens your day, forcing your body to advance its clock—which goes against your natural cycle. Westward travel lengthens your day, aligning with the natural tendency to drift later, making adjustment 30–50% easier.

  • Natural circadian period: ~24.2 hours (slightly longer than 24h)
  • Eastward = shorten the day (harder, against natural drift)
  • Westward = lengthen the day (easier, with natural drift)
  • Recovery eastward takes ~50% longer than westward
  • Body adjusts ~1.5h/day westward but only ~1h/day eastward
Q

Does melatonin help with jet lag?

Yes. Low-dose melatonin (0.5–3mg) taken 2–3 hours before your desired bedtime at the destination helps shift your circadian clock. Research shows it reduces jet lag symptoms by 40–50% when timed correctly. Higher doses (5–10mg) are not more effective and may cause grogginess.

  • Effective dose: 0.5–3mg (higher is not better)
  • Timing: 2–3 hours before desired destination bedtime
  • Reduces symptoms by 40–50% in controlled studies
  • Use for 3–5 days after arrival, then stop
  • Combine with light exposure for fastest adjustment
Q

When should I seek or avoid bright light for jet lag?

For eastward travel, seek bright morning light at the destination to advance your clock, and avoid evening light. For westward travel, seek bright evening light to delay your clock, and avoid morning light. Light is the strongest signal your body uses to set its internal clock.

  • Eastward: seek morning light (7–10 AM), avoid evening light after 6 PM
  • Westward: seek evening light (4–7 PM), avoid morning light before 9 AM
  • Sunlight is most effective; 10,000 lux light therapy lamp as backup
  • Sunglasses can help avoid light at the wrong times
  • Combine light timing with melatonin for 60–70% faster adjustment
Q

Do older people get worse jet lag?

Yes. Adults over 50 recover 20–40% slower from jet lag due to lower melatonin production and reduced circadian flexibility. A 6-zone eastward trip might take 9 days for a 30-year-old but 11–13 days for a 60-year-old. Older travelers benefit more from melatonin supplementation and strict light schedules.

  • Age 50+: 20% slower recovery on average
  • Age 65+: 30–40% slower recovery
  • Melatonin production declines with age
  • Circadian flexibility decreases after 40
  • Older travelers should start schedule shifts 2–3 days before departure

Example Calculations

1New York to Paris (Eastward, 6 zones)

Inputs

Zones Crossed6
DirectionEastward
Age35
Departure6:00 PM local
Arrival8:00 AM local

Result

Recovery Time9 days
SeverityModerate
Seek Light At07:00
Melatonin At20:00
Adjustment Rate1.0h / day

6 time zones eastward at 1.5 days per zone = 9 recovery days. Severity is moderate (4–7 zones). Seek bright morning light at 7 AM Paris time, take melatonin at 8 PM. Your body adjusts about 1 hour per day eastward.

2Tokyo to Los Angeles (Eastward, 8 zones)

Inputs

Zones Crossed8
DirectionEastward
Age55
Departure5:00 PM local
Arrival10:00 AM local

Result

Recovery Time14 days
SeveritySevere
Seek Light At07:00
Melatonin At20:00
Adjustment Rate1.0h / day

8 time zones eastward at 1.5 days per zone = 12 base days. Age factor (55+) adds 20%, rounding to 14 recovery days. Severity is severe (8+ zones). The body adjusts about 1 hour per day eastward, so 8 zones takes the full 14 days to fully resolve.

3London to New York (Westward, 5 zones)

Inputs

Zones Crossed5
DirectionWestward
Age30
Departure9:00 AM local
Arrival12:00 PM local

Result

Recovery Time5 days
SeverityModerate
Seek Light At16:00
Melatonin At22:00
Adjustment Rate1.5h / day

5 time zones westward at 1.0 day per zone = 5 recovery days. Westward travel is easier because the body naturally drifts later. Seek bright evening light at 4 PM New York time to delay your clock, take melatonin at 10 PM.

Formulas Used

Jet Lag Recovery Time

Recovery Days = Zones Crossed × Direction Multiplier × Age Factor

Estimates the number of days to fully adjust to a new time zone.

Where:

Zones Crossed= Number of time zones between origin and destination (1–12)
Direction Multiplier= Eastward: 1.5 (harder), Westward: 1.0 (easier)
Age Factor= 1.0 for age <50, 1.2 for 50–65, 1.4 for 65+

Daily Circadian Adjustment

Adjustment = 1.0–1.5 hours per day

The body shifts its internal clock by approximately 1 hour/day eastward and 1.5 hours/day westward.

Where:

1.0 h/day= Typical eastward adjustment rate (phase advance)
1.5 h/day= Typical westward adjustment rate (phase delay)

Understanding Jet Lag and How to Beat It

1

The Science Behind Jet Lag

Jet lag occurs when your internal circadian clock is out of sync with the local day/night cycle at your destination. Your suprachiasmatic nucleus (SCN) in the hypothalamus controls this clock, responding primarily to light signals from your eyes. When you cross time zones, the SCN needs time to resynchronize—about 1–1.5 hours per day.

The human circadian period is naturally about 24.2 hours, slightly longer than a solar day. This means your body naturally drifts later each day. Westward travel extends your day, working with this drift, while eastward travel shortens your day, going against it. This is why eastward jet lag is consistently 30–50% harder to overcome.

Common jet lag symptoms and their typical timeline
SymptomOnsetDurationManagement
FatigueDay 1Peaks days 2–3Napping 20 min max, light exposure
InsomniaNight 13–7 nightsMelatonin, avoid screens 2h before bed
Digestive issuesDay 1–22–4 daysEat on destination schedule
Difficulty concentratingDay 12–5 daysSchedule critical tasks after recovery
2

Your Recovery Toolkit: Light, Melatonin, and Schedule

Light exposure is the most powerful tool for shifting your circadian clock. For eastward travel, seek 30–60 minutes of bright sunlight between 7–10 AM at your destination to advance your clock. For westward, seek evening light between 4–7 PM to delay it. A 10,000 lux light therapy lamp works when sunlight is not available.

Melatonin (0.5–3mg) taken 2–3 hours before your desired destination bedtime enhances the adjustment from light exposure. Studies show combining timed light with melatonin speeds recovery by 60–70% compared to no intervention. Stop melatonin after 5 days to avoid dependence on the supplement.

  • Eastward: morning light (7–10 AM) + melatonin at 8 PM destination time
  • Westward: evening light (4–7 PM) + melatonin at 10 PM destination time
  • Start shifting sleep 1 hour/day for 2–3 days before departure
  • Eat meals on destination schedule starting on the plane
  • Nap no more than 20 minutes to avoid deep sleep that worsens jet lag
  • Stay hydrated: dehydration amplifies fatigue and headaches

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Last Updated: Mar 25, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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