Foleil helps you look beyond one night's duration and inspect the timing pattern across recorded nights. Sleep regularity is a different question from how long you slept yesterday. The advantage is a trend you can review with its coverage, while missing nights remain gaps in the evidence rather than silently becoming nights spent awake.
How it works
Foleil compares recorded sleep and wake intervals across days to calculate its sleep-regularity view. It requires sufficient eligible day pairs before showing the index. The calculation uses the sleep intervals available to Foleil; naps and awakenings contribute only as far as the saved records describe them. Trend views retain the number of nights with evidence.
Why it matters
Windred and colleagues' Sleep paper (2024) studied sleep regularity and mortality associations in a cohort. That supports regularity as a subject of research, not a prediction of an individual's outcome or validation of Foleil's input data. Foleil's interval-based implementation has the limits of its records. It gives you a way to inspect timing consistency without claiming a medical risk estimate from the resulting index.
Compared with other approaches
Oura's Readiness contributors, reviewed 19 October 2026, include longer-term sleep and activity context. Welltory also documents broad health insights. Foleil's reason here is a coverage-aware regularity view beside the training, food and reflection routine you manage. The comparison does not equate proprietary scores or suggest that other apps ignore sleep timing.
The evidence
Duration averages and regularity answer different questions. Two weeks can have a similar average sleep duration while differing in timing, and missing records can limit either comparison. Foleil's calculation requires eligible pairs rather than treating every absent day as a full day awake. Recorded intervals also differ from a complete minute-by-minute account of sleep states. These limits matter when deciding whether an apparent change reflects your routine or a change in recording coverage.
Put it into your day
When reviewing a week with travel or changed work hours, first inspect which nights have usable records. Look at bedtime and wake timing alongside total sleep, then compare periods with similar coverage. If the index is unavailable, treat that as a need for more evidence rather than a negative judgement. Add a reflection about the week if it helps explain your schedule, without assuming that a pattern establishes its cause. The practical benefit is a more specific conversation about your routine: which recorded times changed, how consistently you recorded sleep and what you want to consider when organising the next week.
Frequently asked questions
Is regularity the same as sleep duration?
No. Regularity concerns the resemblance of sleep and wake timing across days; duration describes time asleep.
Are missing nights counted as awake?
No. Foleil needs eligible recorded day pairs and does not use an absent night as evidence of a whole day awake.
Does the index predict my health outcome?
No. A research association is not an individual prediction, and Foleil’s view is limited by the available recorded intervals.
What if my recording habits changed?
Compare periods with similar coverage where possible. A change in available nights or interval detail can alter what the regularity view can meaningfully describe.
