🌏 Jet Lag Circadian Shift & Recovery Planner
Beat jet lag with a pre-flight sleep shift plan. Get day-by-day bedtime adjustments and light exposure timing for your route and direction of travel.
Go to bed 1 hour earlier each night for 3 days before departure.
Seek bright morning sunlight upon arrival; avoid evening blue light.
What Jet Lag Circadian Shift & Recovery Planner Does
This planner estimates how long your body clock will take to catch up after crossing time zones, and gives the direction-appropriate light and sleep-shift strategy. Enter the size of the shift and whether you are flying east or west.
Direction matters more than distance. The human circadian clock runs slightly longer than 24 hours when left alone, so lengthening a day — flying west — works with it, while shortening one by flying east works against it. That is why the same six zones takes about six days eastbound and about four westbound, and why the same trip feels so different in each direction.
There is a limit to that logic, and it is the thing most jet lag advice gets wrong. Past twelve zones the shorter route round the clock reverses: flying sixteen hours east puts you eight hours behind rather than sixteen ahead, and your body adjusts the easy way regardless of which direction the aircraft flew. This tool used to take the larger number literally and predict sixteen days for that trip. It now reports the six days the adjustment actually takes.
How to Use Jet Lag Circadian Shift & Recovery Planner
- Select travel direction (Eastward vs Westward)
- Enter the time zone difference in hours (e.g. 6 hours)
- Review estimated acclimatization days and pre-flight light/sleep strategies
Formula Used by Jet Lag Circadian Shift & Recovery Planner
Effective shift, and why it is not always the number on your ticket
if zones > 12: effective = 24 − zones, and the direction flips
- zones
- Hours of time difference between origin and destination
- effective
- The shift your circadian clock actually has to make, always 12 hours or fewer
Worked example
Los Angeles to Sydney — an 18-hour eastward difference.
- 18 > 12, so the short way round is the other direction
- 24 − 18 = 6
- Direction flips from east to west
Result: A 6-hour westward adjustment, about 4 days — not the 18 days a literal reading gives. The clock does not know which way the plane flew; it only knows where the light now falls.
Days to adjust
eastward ≈ 1.0 day per zone; westward ≈ 0.7 days per zone
- eastward
- Requires advancing the clock — shortening a day, which the body resists
- westward
- Requires delaying the clock — lengthening a day, which is closer to the body's natural drift
Worked example
A six-hour shift in each direction — New York to London, and back.
- Eastbound: 6 × 1.0 = 6 days
- Westbound: 6 × 0.7 = 4.2, rounded to 4 days
Result: 6 days out, 4 days home, for an identical time difference. These rates are rules of thumb: individual adaptation varies widely and is faster with deliberate light management than without.
Days to Adjust by Zones Crossed
At roughly one day per zone eastward and 0.7 westward. Both columns assume no deliberate light or melatonin strategy.
| Zones crossed | Eastward | Westward |
|---|---|---|
| 3 | 3 days | 2 days |
| 5 | 5 days | 4 days |
| 6 | 6 days | 4 days |
| 8 | 8 days | 6 days |
| 9 | 9 days | 6 days |
| 11 | 11 days | 8 days |
| 12 | 12 days | 8 days |
Past Twelve Zones, the Short Way Round Reverses
The adjustment your clock makes is never more than twelve hours. The final column is what a calculator that takes the ticket literally reports — including this one, until this batch.
| Time difference | Direction flown | Effective adjustment | Days | What a naive reading says |
|---|---|---|---|---|
| 13 hours | East | 11 hours westward | 8 | 13 |
| 14 hours | East | 10 hours westward | 7 | 14 |
| 16 hours | East | 8 hours westward | 6 | 16 |
| 18 hours | East | 6 hours westward | 4 | 18 |
| 16 hours | West | 8 hours eastward | 8 | 11 |
Real Routes
Worked through the rules above. Note that the longest flight is not the worst adjustment.
| Route | Difference | Effective adjustment | Estimated days |
|---|---|---|---|
| New York → London | 5 east | 5 hours eastward | 5 |
| London → New York | 5 west | 5 hours westward | 4 |
| London → Sydney | 10 east | 10 hours eastward | 10 |
| New York → Tokyo | 14 east | 10 hours westward | 7 |
| Los Angeles → Sydney | 18 east | 6 hours westward | 4 |
How to Read Your Result
Light does opposite things depending on when it lands
The rule underneath all jet lag advice is the phase response curve. Light in the hours BEFORE your core body temperature minimum — roughly a couple of hours before your usual wake time — delays your clock, pushing you later. Light AFTER it advances your clock, pulling you earlier. Eastward travel needs advances, so you want light after that point and darkness before it; westward travel needs delays, so the reverse. This is why "get morning sunlight on arrival" is good advice for a modest eastward trip and can be actively counterproductive for a large one: cross eight or more zones east and local morning light may still be falling before your body's temperature minimum, delaying you in exactly the wrong direction.
Start before you fly, not after you land
Shifting your sleep by an hour a night for a few days before departure means arriving with part of the adjustment already made, and it is the single highest-value thing on this page. Going east, go to bed and get up an hour earlier each night; going west, an hour later. Three days of that removes roughly three days of the estimate. It is also the part travelers skip, because it happens while they are still busy at home.
Jet lag and travel fatigue are different problems
Feeling wrecked after a long flight is not necessarily jet lag. Dehydration, a cramped cabin, a short night and alcohol produce travel fatigue, which resolves with one decent night of sleep. Jet lag is specifically the mismatch between your internal clock and local time, and it resolves at roughly the rates above no matter how well you slept on the plane. Flying north-south across no time zones can leave you exhausted with zero jet lag — which is a useful test of which one you actually have.
Melatonin is a clock signal, not a sleeping pill
A Cochrane review found melatonin effective for preventing or reducing jet lag on flights crossing five or more zones. Its usefulness depends on timing rather than dose — taken at the wrong point in your cycle it shifts the clock the wrong way, which is the same trap as mistimed light. It is regulated as a dietary supplement in the US rather than as a medicine, so strength and purity vary between products. This tool does not schedule melatonin; if you plan to use it, time it deliberately against the direction of travel.
Limitations & Accuracy Notes
- No day-by-day schedule. Competing tools generate hour-by-hour light, sleep and melatonin plans; this gives a duration estimate and direction-appropriate strategy, not an itinerary.
- No chronotype input. Whether you are a natural early riser or a night owl shifts your temperature minimum and therefore the timing of every light recommendation — the leading jet-lag app is built around exactly that.
- Takes a time difference rather than a flight. It does not read departure and arrival times, layovers, flight duration, or the direction the sun is traveling relative to you.
- The one-day-per-zone rates are population rules of thumb. Individual adaptation varies substantially, is generally slower with age, and is faster with deliberate light management than the table assumes.
- No melatonin dosing or timing schedule, and no caffeine strategy.
- Does not distinguish jet lag from travel fatigue, and cannot account for a trip short enough that staying on home time is the better plan — for a two-day trip, adjusting at all is often the wrong call.
Frequently Asked Questions
Why is eastward travel associated with worse jet lag?
How long does it take to fully recover from jet lag?
Why is flying east harder than flying west?
How long does adjustment take?
Does light exposure actually help?
Should I use melatonin?
Should I nap on arrival?
Is my travel data stored?
References & Further Reading
- Eastman CI, Burgess HJ — How To Travel the World Without Jet Lag, Sleep Med Clin 2009;4(2):241-255 — The practical reference for pre-flight phase shifting and for timing light against the core body temperature minimum by direction of travel
- Duffy JF, Czeisler CA — Effect of Light on Human Circadian Physiology, Sleep Med Clin 2009;4(2):165-177 — The phase response curve: why light before the temperature minimum delays the clock and light after it advances the clock
- Herxheimer A, Petrie KJ — Melatonin for the prevention and treatment of jet lag, Cochrane Database Syst Rev 2002;(2):CD001520 — Systematic review finding melatonin effective for jet lag when crossing five or more time zones, with timing mattering more than dose