When the plan meets the trip: how check-ins re-pace a jet lag schedule
A jet lag plan assumes you follow it, and on a real trip you rarely follow it exactly. Jetlag Away asks once a day whether you kept to the sleep plan and how much energy you have, and from the second check-in on it re-paces the remaining days: slower if the plan is not being kept, with a nap back on offer if you are keeping it and still struggling. Nights already past are never rewritten.
The first day of a trip rarely goes as written. A delayed departure, a meeting that ran late, a hotel room that would not go dark. A schedule calculated before you left cannot know about any of that, and a schedule that carries on as if it had all gone to plan will be wrong for the rest of the trip.
Why a static schedule drifts
Every jet lag plan is built on an assumed rate: how many hours a day your body clock moves, given the plan’s light timing is followed. Jetlag Away’s rates run from an hour a day advancing on gentle to two hours a day delaying on aggressive. How a plan is built has the table.
The words that matter are “given the plan is followed”: sleep at the planned times, light at the planned hours. The two work together. In one study, moving sleep an hour earlier each day shifted the clock about 0.6 hours in dim light, against 1.5 to 2.1 hours with bright morning light [BC03]. Miss the parts of the plan that do the moving and the clock moves less, and the plan’s idea of where your body clock is runs ahead of where it actually is.
When that happens, the light windows for the following days are placed for a clock that is further along than yours. A conservative plan is forgiving of that for a while, but not indefinitely.
What the check-in asks
Once a day, the Plan screen asks “How are you adapting today?”. The check-in takes a few seconds:
- Mood, from “Restless” to “Energized”.
- “Did you follow yesterday’s sleep plan?”, yes or no. This is the part you can answer reliably, and it is the one the plan acts on most.
- Energy, from 1 to 10.
There is one check-in per day, by your phone’s date, and you can edit today’s. The answers are stored with your account. They are not free text; there is nowhere to type a note.
What it changes
From the second check-in, the plan rebuilds the remaining days from what you reported over the last week of this trip:
- The pace follows how often you kept to the plan. The plan’s rates are scaled between half and full speed by the share of check-ins where you answered yes. Follow it every day and nothing changes. Follow it half the time and the plan assumes three-quarters of its normal pace.
- The pace never drops below half. Even unaided, the clock drifts towards local time, so the plan does not assume you have stopped moving.
- A nap can come back. If you have been following the plan at least seven times in ten and your average energy is four out of ten or lower, the arrival-day nap is switched back on, even on the aggressive setting. Effort without relief is a sign the plan is asking too much.
Mood is recorded and shown on the Plan screen, but it does not change the plan. Only the two answers the model can act on do.
A slower pace means more days. Five hours still to shift at the moderate advancing rate of 1.25 hours a day is four days of light windows. At three-quarters of that pace it becomes six.
After you save, the check-in tells you which way it went: “Good — your body clock is moving at the pace the plan assumed,” or “Travel happens. Your remaining schedule will be re-paced around it.”
Forward only
A check-in never touches the nights before your flight or the flight itself: those come from the trip and from the moment the plan was first made, so a check-in re-paces only the days after landing. And no rebuild of any kind moves a night that has already happened. A plan that quietly re-dated last night’s sleep would make the timeline meaningless as a record of what you were asked to do.
The other ways a plan rebuilds
Check-ins are one of four triggers:
- Your flight changes. “Edit trip”, then “Save changes”, and the plan is rebuilt around the new times. A delayed departure becomes a different plan, not a stale one.
- Your settings change. If you change your usual hours, your limits or the intensity, the Plan screen says “Your settings changed since this plan was made.” and offers “Update plan”.
- You ask for it. “Regenerate my plan” in the Account screen does the same on demand.
- You check in, as above.
Whichever it is, reminders follow automatically. The phone’s queue is rebuilt from the new plan, so no reminder from the old version fires.
What it cannot do
The check-in is a report, not a measurement. The app cannot see your light exposure or your body clock; it has your answers and its model. So:
- The re-paced plan is still an estimate. The progress ring and the Circadian Trajectory chart are the model’s view of where you are, and the chart says so.
- One bad night does not swing the plan. Below two check-ins nothing changes, by design.
- Honest answers make a better plan. Answering “yes” to keep the original pace only means the light windows aim at a clock you do not have.
None of this makes the plan clever. It makes it less wrong for longer, which on a trip across several time zones is most of what a schedule can offer. The core body temperature minimum explains why a window aimed at the wrong clock matters.
Sources
- [BC03] Burgess HJ, Crowley SJ, Gazda CJ, Fogg LF, Eastman CI. Preflight adjustment to eastward travel: 3 days of advancing sleep with and without morning bright light. Journal of Biological Rhythms, 2003.
Jetlag Away is a scheduling tool and not medical advice. If you have a sleep or circadian disorder, or any diagnosed condition affected by sleep, talk to a healthcare professional first — see the health disclaimer in our terms.
Last reviewed 10 October 2026. Published 10 October 2026.