Jet-Lag Recovery & Light Planner
Jet-lag calculator — enter how many time zones you are crossing and the direction to estimate your recovery time and get a tailored light and sleep strategy to adjust faster. A practical planner for long-haul travellers. Runs in your browser.
Jet-Lag Recovery & Light Planner
How to Use the Jet-Lag Calculator
Pick your direction
Choose eastward or westward — it changes both the recovery time and the strategy.
Set time zones crossed
Enter how many zones your trip spans, not the flight length.
Read the recovery time
See the estimated days to adjust and your tailored light-and-sleep strategy.
Prepare before you fly
Start shifting your clock a few days early and follow the tips on arrival.
Beating Jet Lag
Jet lag is the price of crossing the planet faster than our biology was built for. Deep in the brain sits a master clock that runs on a roughly twenty-four-hour cycle, governing when we feel sleepy and alert, when we digest food, and when key hormones rise and fall. Fly across several time zones and that clock is suddenly out of step with the world outside: it is calling for sleep when the destination wants you awake, and vice versa. The result is the familiar fog, broken sleep and daytime exhaustion that lingers until the clock resets. This tool estimates how long that takes using the well-established rule of thumb — about a day of recovery for each time zone crossed travelling east, and roughly two-thirds of a day per zone travelling west.
That east-west asymmetry surprises people, but it follows from how our clock works. Flying east shortens your day and forces you to sleep and wake earlier than your body wants, and the human circadian system finds it genuinely harder to advance than to delay. Flying west lengthens your day, asking you to stay up later, which sits closer to our natural drift toward later hours — so westward trips are usually easier to shake off. It is also worth remembering that jet lag is driven by time zones, not flight hours: a long flight that stays in roughly the same longitude causes little lag, while a shorter hop across several zones can flatten you.
The encouraging part is how much you can do to shorten the recovery, and the calculator turns its estimate into a direction-specific plan. Light is the single most powerful lever for resetting the clock, so the strategy tells you when to seek it and when to avoid it: chase bright morning light after flying east, and bright evening light after flying west. Shifting your sleep schedule an hour or so toward the destination in the days before departure closes part of the gap in advance, switching to local time the instant you board trains your mind onto the new schedule, and short naps under thirty minutes restore alertness without sabotaging the night. None of this is medical advice — recovery varies with age, sleep quality and preparation, and anyone with a sleep disorder should seek personalised guidance — but for most travellers these basics genuinely work. Everything is computed in your browser, so nothing you enter leaves your device.
Jet lag is set by time zones, not flight hours — and light, timed for your direction, is the fastest way to reset.
10 Facts About Jet Lag
Jet lag comes from your body clock lagging local time.
Recovery is roughly 1 day per time zone going east.
Going west is easier — about ⅔ day per zone.
Flying east shortens your day; west lengthens it.
Crossing fewer than 3 zones rarely causes much lag.
Daylight is the most powerful clock-resetting cue.
Seek morning light going east, evening light going west.
Adjusting sleep before you fly shortens recovery.
Short naps under 30 minutes help without wrecking night sleep.
This calculator runs in your browser — nothing is uploaded.
Frequently Asked Questions
- Jet lag happens when you cross time zones faster than your internal body clock can adjust. Your circadian rhythm — the roughly 24-hour cycle that governs sleep, alertness, digestion and hormones — is still set to your origin, so it clashes with the new local time, leaving you sleepy, foggy and out of sync until it catches up.
- As a rule of thumb, recovery takes about one day per time zone crossed when travelling east, and roughly two-thirds of a day per zone going west. So a six-zone eastward trip might take around six days to fully shake off, while the same trip westward is quicker. The calculator applies this to your zones and direction.
- Because flying east shortens your day — you have to fall asleep and wake earlier than your body wants — and the human clock finds it harder to advance than to delay. Flying west lengthens your day, asking you to stay up later, which is closer to our natural tendency to drift later, so it is generally easier to adjust.
- The most powerful tool is light at the right time: seek bright morning light when you have flown east and bright evening light when you have flown west, and avoid light at the opposite end. Shift your sleep schedule a little toward the destination in the days before you fly, switch to local time the moment you board, and stay hydrated while limiting alcohol and caffeine.
- Adapting to the local schedule quickly helps, so getting daylight and staying active during destination daytime is good. But fighting extreme tiredness entirely can backfire; a short nap of under thirty minutes, taken before mid-afternoon, can restore alertness without stealing from your night’s sleep. The aim is to nudge your clock, not to martyr yourself.
- Yes. Jet lag is driven by the number of time zones you cross, not the hours in the air. A long north-to-south flight that stays in roughly the same zone causes little jet lag despite the distance, while a shorter east-west flight across several zones can hit hard.
- A few days before departure is ideal. Gradually shifting your bedtime and wake time an hour or so toward the destination — earlier for eastward travel, later for westward — means your body has less of a gap to close on arrival, which can noticeably shorten recovery.
- Many travellers find correctly-timed melatonin useful for adjusting the clock, and light therapy is well supported, but timing and suitability vary by individual and any sleep medication should be discussed with a pharmacist or doctor. This tool focuses on the behavioural basics — light, schedule and naps — which are effective and risk-free for most people.
- No. It is a general travel-planning estimate of recovery time with practical, widely-recommended strategies. Individual recovery varies, and anyone with a sleep disorder or relevant health condition should seek personalised advice from a healthcare professional.
- Completely free, with no account or usage limit. It runs entirely in your browser, collects no data, and works offline once the page has loaded.
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