JetShift: Jet Lag Calculator

Getting a plan

Add the flight you are about to take: the city you leave, the city you land in, and the departure and arrival times printed on your ticket. JetShift works out how far your body clock has to move and builds a schedule of light, sleep, caffeine and — if you use it — melatonin.

Why the plan starts before I fly

A body clock moves roughly an hour a day. Waiting until you land means spending the first days of the trip adjusting. Starting two or three days early means arriving most of the way there. You choose how many days of preparation you are willing to do, from none up to five.

Why is it shifting me the wrong way?

This surprises people, and it is deliberate. Going east means moving your clock earlier, which the body manages at about an hour a day. Going west means moving it later, which it manages at about an hour and a half a day. Because those rates differ, a long eastward trip is sometimes quicker to solve by going the long way round.

It says there is nothing to shift

The two cities are less than an hour apart on the body clock, so there is nothing worth planning. Keep your normal sleep window and you will be fine on arrival.

Reading the plan

Each day is one bar, waking to waking

A day card runs from the morning you wake to the following morning, not from midnight to midnight — so a night's sleep sits whole in one card instead of being cut in half. The wide lane shows sleep and light; the thin lane below shows caffeine and melatonin. Tap a card to see every step written out with its times.

The times jumped by several hours between two cards

That is the arrival, and it is not a bug. Up to the flight the plan is written in your home city's time; from the moment you land it switches to the destination's. Each card names the city it is written in, next to the date — look for Mon, Aug 3 · Tokyo.

Bright light and avoiding light

Light is the part that actually moves the clock; sleep timing alone will not do it. Light after your body temperature minimum — roughly two hours before you normally wake — pulls the clock earlier, and light before it pushes the clock later. That is why an eastward plan asks for light first thing in the morning and darkness in the evening, and a westward plan asks for the opposite.

Melatonin only appears on some plans

It is shown for eastward plans, where a low dose a few hours before the target bedtime helps pull the clock earlier, and only if you turned it on for that trip. Westward plans do not use it. JetShift is a planning tool, not medical advice — talk to a doctor before taking melatonin.

Reminders

I am not getting any

Reminders are part of the full version. Open a trip's plan and tap the bell in the top right — that is where JetShift asks for notification permission, and it does not ask before then. If you declined earlier, iOS will not ask again: turn it on in the iOS Settings app under Notifications → JetShift, then toggle Step reminders in JetShift's own Settings tab.

How far ahead do they go?

Each reminder arrives ten minutes before its step, in the time zone that step belongs to. iOS allows an app at most 64 pending notifications, so JetShift schedules the next 60 steps and refreshes them when you open the plan. On a long trip, open the app every few days.

Trips, sync and the widget

Do my trips sync between devices?

Yes, through your own private iCloud. Sign in to the same Apple Account on both devices and keep iCloud Drive on. If iCloud is unavailable, JetShift keeps everything locally instead — you will not lose anything, it simply will not appear on the other device.

The widget is blank or showing the wrong trip

The widget shows the trip you are living through — the one whose plan window contains today — and otherwise the next one to start. If no plan is active it shows nothing to do, which is the honest answer. It refreshes when you open the app, so open JetShift once after adding or editing a trip.

Changing or deleting a trip

Swipe a trip left in the list to delete it. Deleting removes it from iCloud too, on every device. To change your usual sleep times for a single trip, edit them on that trip — the answer you gave when you first opened the app is only the starting point.

Purchase

What is free and what is not

The time zone calculator is free and complete: compare any two cities on any date, with daylight saving applied for the exact day you pick. Every trip shows its summary and the first two days of its plan. The full schedule, step reminders and unlimited saved trips are one payment — not a subscription. You fly a few times a year; paying every month for that would be absurd.

I paid, but a device says it is locked

Open Settings inside JetShift and tap Restore purchase. The unlock is tied to the Apple Account that bought it, and it is Family Sharing enabled, so household members can use it too. If it still does not unlock, email us with the date of purchase and we will sort it out.

Requirements

Platform

iPhone and iPad

Minimum OS

iOS 18.6 or later

Languages

English, Chinese (Simplified), French, German, Japanese, Korean, Norwegian, Portuguese (Brazil), Spanish

Account

None required

Price

Free to download, one-time unlock — no subscription, no ads

Data

Stays on your device and in your own iCloud

Developer

frekvens.ai