Titan builds one sleep session for each day from the sleep samples in Apple Health. This article covers how samples join into a session, which day a session belongs to, how Titan picks between two sessions on the same day, and how it combines samples from more than one tracker.
Your Sleep and Recovery numbers on Today both read this one session. If a night looks wrong or missing, the rules below usually explain why.
01Samples less than 2 hours apart join one session
Apple Health stores sleep as separate samples marked In Bed, Awake, Core, Deep, REM, or Asleep. Titan sorts every sample by start time and walks through them in order. A sample that starts within 2 hours of the latest end time so far joins the current session. A sample that starts more than 2 hours later begins a new session.
Say your watch records sleep from 11:00 PM to 3:00 AM, then again from 4:30 AM to 7:00 AM. The gap is 90 minutes, so Titan treats 11:00 PM to 7:00 AM as one night. The 90 minutes with no samples show as a gap on the timeline. They add nothing to your time asleep.
If the second stretch had started at 5:30 AM, the gap would be 2.5 hours. Titan would then see two separate sessions and apply the tie-break described below.
02A session belongs to the day it ends, up to noon
Titan assigns each session to the calendar day it ends on, in your phone's local time. The session must end after midnight and no later than 12:00 PM. A session that ends after noon counts for no day at all.
This rule decides a few common cases.
- A normal night from 11:00 PM to 7:00 AM counts for the day you wake up.
- An early night from 8:00 PM to 12:30 AM counts for the new day, since it ends after midnight.
- An afternoon nap from 2:00 PM to 3:00 PM is ignored because it ends after noon.
- A late sleep from 4:00 AM to 12:30 PM is ignored because it ends 30 minutes past noon.
Shift work
If you sleep during the day after a night shift, the noon cutoff matters. Sleep from 3:00 AM to 11:00 AM counts for that day. Sleep from 8:00 AM to 4:00 PM ends after noon, so Titan does not use it, and that day will show no sleep. The missing sleep article covers what you see when this happens.
03The session with the most sleep wins
More than one session can end on the same morning. A night and a separate morning nap that both finish before noon are the usual example. Titan keeps only one of them for the day. It picks the session with the most time asleep.
Time asleep is the sum of Core, Deep, REM, and Asleep time. Awake time and In Bed time do not count toward it. A session with 10 hours in bed and 5 hours asleep loses to a session with 6 hours in bed and 5.5 hours asleep. If two sessions tie to the second, Titan keeps the earlier one.
The session Titan does not pick is left out of that day entirely. Its sleep does not add to your total or your sleep debt.
04How overlapping sources merge
When more than one app or device writes sleep to Apple Health, their samples often cover the same minutes. Titan does not add the overlapping minutes twice. It cuts the night into slices at every point where any sample starts or ends. For each slice it keeps the one stage with the highest priority among the samples that cover it.
| Priority | Stage |
|---|---|
| 1, highest | Awake |
| 2 | REM |
| 3 | Deep |
| 4 | Core |
| 5, lowest | Asleep, no stage given |
A tracker that reports stages beats one that only reports Asleep for the same minutes. Awake beats every sleep stage, so a wake-up that one tracker records and another misses still shows as awake time. Any slice that no stage sample covers stays a gap.
In Bed samples merge separately. Titan joins every overlapping In Bed sample into one continuous span, so two trackers that both log 11:00 PM to 7:00 AM in bed count as 8 hours in bed.
The session detail shows one source name. That name is the app or device that wrote the most samples in the session.
05When a Sleep Tracker is selected
You can pick a preferred tracker in Settings > Recovery & Sleep > Sleep Preferences > Sleep Tracker. You reach Settings from the avatar on Today, then You > Settings.
Once you pick one, Titan builds sessions from that tracker's samples first. The merge rules above then apply only within that tracker's data. On any day where your chosen tracker has no session, Titan falls back to all your sleep sources for that day. If you have chosen specific sources for sleep in your data source settings, those choices take priority and the Sleep Tracker filter is skipped. The sleep source article covers both settings.
For questions this article does not answer, use the contact page.
