"How long until I feel normal?" Most jet-lagged travelers ask this on day 2 of feeling like garbage. The answer follows a rough rule: about one day of recovery per hour of time-zone shift, eastbound; about two-thirds of a day per hour, westbound. Your age, fitness, and sleep habits modify this.
The basic rule
- Eastbound: ~1 day per hour of time difference. NY → London (5h) = ~5 days. NY → Tokyo (14h)... but the formula breaks down past 12 hours, which we'll get to.
- Westbound: ~0.67 day per hour. Same NY → Tokyo westbound on the return = ~9 days vs the 14 it would take eastward.
So for a 1-hour shift (e.g., daylight savings or a short trip): ~1 day. For a 5-hour shift (NY/Europe): ~5 days east, ~3 days west. For a 12-hour shift (NY/Asia): ~12 days east, ~8 days west.
Why the formula breaks at 12+ hours
Crossing 12+ time zones flips day and night. Your body has two options for adjustment:
- Push the clock forward 12 hours (eastbound adjustment).
- Push the clock backward 12 hours (westbound adjustment).
Both end up at the same spot on the clock. Your body picks the easier path — usually westbound (~0.67 days per hour). So a 14-hour east shift may actually adjust like a 10-hour west shift, taking ~7 days instead of 14.
This is why people often describe Tokyo trips as "weirdly easy in some ways" — the body sometimes shortcuts the adjustment.
Worked examples
| Route | Hours | East days | West days |
|---|---|---|---|
| NY → Chicago | 1 | 1 | 0.6 |
| NY → Denver | 2 | 2 | 1.3 |
| NY → London | 5 | 5 | 3.4 |
| NY → Paris | 6 | 6 | 4 |
| NY → Cairo | 7 | 7 | 4.7 |
| NY → Mumbai | 10.5 | 10.5 | 7 |
| NY → Tokyo | 14 (or 10 west) | 14 / ~10 | 9.4 |
| NY → Sydney | 15 (or 9 west) | 15 / ~9 | 10 |
For very long flights, your body picks the shorter direction.
What "fully adjusted" means
Recovery is gradual. You don't wake up on day 5 suddenly normal. Symptoms fade roughly linearly:
- Day 1: severe — you'll be fatigued, foggy, and probably wake up too early or too late.
- Day 3: ~50% — sleep starts feeling more normal but you're still tired during your usual peak hours.
- Day 5–6: ~85% — you're functional but might still notice some afternoon dips.
- Day 7: usually fully adjusted for trips up to 6 hours of zone shift.
For longer shifts (12+ hours), full adjustment can take 1.5+ weeks.
Age slows recovery
Studies consistently show:
- Under 30: 0.85 × the standard formula days
- 30–50: 1.0 × (the baseline)
- 50+: 1.2–1.4 ×
So a 60-year-old recovering from a 6-hour east shift might take 7–8 days vs the 6-day baseline. The effect comes from older adults' slower hormonal adaptation.
Fitness and sleep habits modify recovery
Regular exercise: ~10% faster recovery according to some studies.
Consistent home sleep schedule: faster adjustment because the circadian clock is more stable. Erratic sleepers struggle more with jet lag.
Light exposure habits: people who routinely get morning outdoor light recover faster (their light-sensitivity is higher).
Alcohol/caffeine use: heavy use slows recovery.
Subjective vs objective recovery
Two types of recovery happen at different speeds:
- Subjective: when you stop "feeling" jet lagged. Usually 5–7 days for transcontinental.
- Objective: when your hormone cycles, body temperature rhythm, and digestive timing fully sync to local time. Usually 8–14 days.
For a typical 1-week vacation, you may feel okay by mid-week but never fully objectively adjust. Your body reverses the journey just as you finish adapting.
Round-trip math
If your trip is shorter than the recovery time, you don't fully adjust. A 4-day trip from NY to Tokyo means you arrive jet-lagged, never fully adjust, and then have to readjust on return. Total disruption can be 3+ weeks for a single short trip.
For trips under 5 days going east 6+ hours, some travelers don't even try to adjust — they stay on home time as much as possible.
The "every other day" approximation
For typical 5–8 hour shifts, the rough rule "you'll feel half-adjusted every other day" works reasonably:
- Day 1: 0% adjusted
- Day 2: 25%
- Day 3: 50%
- Day 4: 75%
- Day 5–6: ~95%
This is enough precision for trip planning.
Estimate your trip
Our jet lag calculator takes time-zone difference, direction, and age to give a personalized estimate. Use it to plan when to schedule the most-demanding parts of your trip — first day for low-stakes activities, peak performance days for important meetings.