How Easy2Fly makes a plan

Your body clock and its low point

Most of jet lag comes from a body clock that sits at the wrong hour for the place you land (Waterhouse 2007). Your clock runs a little over 24 hours, 24.18 on average in careful laboratory measurements (Czeisler 1999), and light resets it each day.

The clock has a low point, when your core body temperature bottoms out and you feel sleepiest. For people who sleep eight hours, it falls about three to four and a half hours before they wake (Eastman and Burgess 2009). Easy2Fly estimates your low point from your usual bedtime and wake time, and the plan times each step from that estimate.

Why light leads the plan

Light reaches the clock through your eyes, and its effect depends on timing. Light before the low point moves the clock later. Light after it moves the clock earlier. In a laboratory study of 21 people, 6.7 hours of bright light (about 10,000 lux) at different points of the cycle produced a five-hour swing from the strongest delay to the strongest advance (Khalsa 2003).

Short exposures work: one hour of bright light (about 8,000 lux) produced about 40% of the effect of the 6.7-hour exposure, in 15% of the time (St Hilaire 2012). Ordinary room light also counts: in a 6.5-hour evening exposure, about 100 lux gave half the delay that 9,000 lux did (Zeitzer 2000). Reading on a light-emitting tablet before bed shifted the clock later than a printed book did (Chang 2015).

Daylight outdoors runs from 10,000 to 100,000 lux, far above a lit room (Eastman and Burgess 2009), so go outside for a Bright light step when you can. Mistimed light works against you: more bright light before your low point than after it can move the clock the wrong way (Eastman and Burgess 2009). The plan asks for bright light on the helpful side of your low point, ordinary light beyond it, and dim light where light would hurt.

Why east is harder than west

Fly east and your clock has to move earlier. Fly west and it has to move later. Your clock runs long, so it drifts later on its own, and later is the easier direction. Early field estimates from real travelers are 92 minutes a day after westward flights and 57 minutes a day after eastward flights (Eastman and Burgess 2009).

A very large eastward change adds a complication: the clock can turn the long way round. A published rule of thumb advances the clock for up to about seven time zones east and delays it for eight or more, with exceptions such as night owls (Eastman and Burgess 2009). Easy2Fly chooses the direction for large changes by its own rule and tells you which way it chose.

You can start before an eastbound flight. In a laboratory study, three days of moving sleep one hour earlier each day, with morning bright light, advanced the clock by a median of 1.4 hours. Two hours earlier each day did no better, because the clock could not keep pace (Eastman 2005). Revell and Eastman 2005 set out a preflight plan on this idea.

What melatonin does and does not do

Melatonin does two jobs: it can make you sleepy, and it moves the clock. The clock effect depends on timing. A dose in the afternoon on your body clock moves the clock earlier, and a dose soon after you wake moves it later (Burgess 2010). Around your normal bedtime, a dose does little to the clock (Eastman and Burgess 2009).

The plan places the dose at the start of your sleep on the plane and at bedtime on each night at the destination. After an eastbound flight your clock still runs on home time, so destination bedtime falls in your body’s afternoon or early evening, where a dose moves the clock earlier. A 2002 Cochrane review found that in eight of ten trials, melatonin taken near the destination bedtime (10 pm to midnight) reduced jet lag after flights across five or more time zones. The review judged the benefit likely to grow with the number of zones and to be smaller after westward flights (Herxheimer and Petrie 2002).

Those trials used 0.5 to 5 mg with similar results. Doses above 5 mg appeared no better, and a 2 mg slow-release tablet did worse than fast-release melatonin. Easy2Fly’s melatonin step suggests a low dose, about 0.5 to 3 mg, of a fast-release product with no other ingredients.

Melatonin is optional, and the plan works without it, though it may take longer. A dose at the wrong time can make you sleepy at the wrong hour and slow your adjustment (Herxheimer and Petrie 2002). Side effects at these doses are usually mild: sleepiness, headache, vivid dreams and nausea.

Take only the doses the plan marks, and stop when the plan ends. For adults the NHS names one 3 mg standard tablet for jet lag and limits a prescription to 5 days. Supplement contents vary: a 2023 study found labeling errors in 22 of 25 melatonin gummies (NCCIH 2024). In the US melatonin is a supplement, while the UK and several other countries require a prescription (NHS; NCCIH 2024). Check the rules where you are going.

What caffeine does and does not do

Caffeine blocks adenosine receptors in the brain, and you feel more alert (Magkos 2005). It does not repair a misaligned clock: stimulants raised alertness and performance without returning them to normal while the misalignment lasted (Eastman and Burgess 2009).

Late caffeine can also push the clock later. In a double-blind study, a dose equal to a double espresso three hours before bedtime delayed the melatonin rhythm by about 40 minutes, close to half the delay from three hours of bright evening light (Burke 2015). Eastbound, that is the wrong direction. Caffeine also costs sleep: 400 mg taken six hours before bed still disrupted it (Drake 2013).

Caffeine’s half-life is around three to five hours for many adults and runs from 2.5 to 10 hours between people (Magkos 2005). As of this version, the planner stops caffeine nine hours before a main sleep, a margin over the six hours in the Drake study. Stay within your usual amount and any limit your clinician has given you.

Sleep, including on the plane

The plan puts sleep where it supports the shift: at your bedtime at the destination, and on the plane when the flight crosses the right hours. A day makes up most of a lost night, while jet lag can last much longer (Eastman and Burgess 2009), so a rough night on the plane costs less than a clock left on the wrong time.

Sleep in a dark room or wear an eye mask, because light that reaches your eyes at the wrong point of the cycle can push the clock the wrong way (Eastman and Burgess 2009). If you cannot sleep on the plane, rest and rejoin the plan at the next step.

Daylight saving and half-hour time zones

Easy2Fly plans on the clock of each place you pass through, then converts each step to the true moment using that place’s daylight-saving rules. The rules come from your device’s own time zone data, so nothing needs a connection.

Zones that sit on the half hour or quarter hour, such as India (UTC+5:30), Nepal (UTC+5:45) and Newfoundland (UTC−3:30), get finer time steps.

What we calibrated and what we did not

The numbers that turn the principles above into hours belong to Easy2Fly’s own planner. We calibrated it on five reference flights: San Francisco to London, the same flight with melatonin and with a two-day early start, and London to San Francisco, with and without melatonin.

Other routes follow the same principles, but we have not compared them with another app. These parts go beyond the five references:

• Any route other than San Francisco and London.
• Bedtimes other than 23:00 and sleep lengths other than eight hours.
• Time zones on the half hour or quarter hour.
• Early starts before a westbound flight.
• Journeys with stopovers.
• The choice of direction for very large time changes.

What the planner assumes

No trial has tested whether an Easy2Fly plan shortens jet lag; the cited studies tested the underlying rules on volunteers. As of this version, the planner assumes:

• Your low point sits two hours before your usual wake time. Published averages put it three to four and a half hours before, so yours may come earlier.
• Bright light runs up to six awake hours on the helpful side of the low point, with ordinary light for the six hours beyond.
• Your clock moves two hours a day, or three hours a day with melatonin. Published planning figures are 1.5 hours a day earlier and 2 hours a day later with well-timed light (Eastman and Burgess 2009). If your clock lags the plan, keep following the light and sleep steps.

Who should not use it

Easy2Fly is for healthy adults aged 18 and over. It gives general guidance, not medical advice, diagnosis or treatment, and it is not for pilots or flight crew on duty. If you have a health condition or take medicine, talk to your doctor before you follow a plan.

Ask a doctor or pharmacist before you use melatonin if you take any medicine or supplement, are pregnant or breastfeeding, have epilepsy, take a blood thinner such as warfarin, have liver or kidney problems, or have an autoimmune condition. The NHS lists sleeping pills and other sedatives, some antidepressants, blood-pressure medicines and hormonal contraceptives among the medicines that interact with it (NHS; NCCIH 2024; Herxheimer and Petrie 2002).

Try melatonin at home before you fly. Allow about eight hours after a dose before you drive, drink alcohol or do anything that needs full alertness. Eight hours is a cautious rule of thumb, and the NHS says to avoid driving and machinery whenever you feel sleepy or dizzy.

How to read your plan

The Now card shows what to do right now, with the next three hours below it. Tap a step to see its reason. Ticking a step off changes nothing else, and you can skip any step that clashes with your day.

• Bright light. Go outside, or sit near a bright window with the lights on. Leave sunglasses off.
• Everyday light. Ordinary daylight or a lit room. Stay out of dim places.
• Low light. Keep lamps and screens low. Wear dark sunglasses outdoors, and take them off when you need a clear view, as when you drive or take stairs.
• Sleep. Aim for a dark, cool, quiet room. Use a mask or earplugs if they help.
• Nap. Optional. It appears only if you switch naps on.
• Melatonin. A single dose time, shown only if you chose melatonin. Read the cautions first.
• Caffeine. The window when coffee or tea helps you stay alert.
• No caffeine. The window to skip it, so it does not cost you sleep or push your clock later.