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How the sleep score is calculated

The sleep score is a 0–100 reference score combining duration (50%), deep-sleep share (25%), REM share (15%) and sleep efficiency (10%), each read against your own trailing 28-day baseline — because Apple Health gives you sleep stages but no score.

Inputs and weights

  • Total sleep duration — 50%
  • Deep sleep as a share of total sleep — 25%
  • REM as a share of total sleep — 15%
  • Sleep efficiency (asleep ÷ time in bed) — 10%

Why stages are scored as shares, not minutes

If deep sleep were scored in absolute minutes, a uniformly longer night would earn credit twice for the same fact — once through duration, then again because deep minutes scale with it. A short night would be penalised twice over.

So stages are scored as a share of total sleep, which keeps "slept long" and "slept well" as separate facts.

What counts as total sleep

Total sleep is the sum of every asleep stage (unspecified + core + deep + REM). Time in bed and awake time are excluded — they are not sleep.

This is worth spelling out because it is a trap: Apple Health's "unspecified asleep" field happens to equal the whole night on devices that do not report stages, but is only a fragment on devices that do. Reading it alone understates sleep substantially for half of users.

Limitations

  • Consumer sleep staging still differs meaningfully from polysomnography, deep and REM especially. That is why stages carry only 40% of the weight and duration — the most reliable part — carries 50%.
  • When only deep or REM data exists without a bulk sleep stage, we withhold the score rather than compute a confident-looking low number from fragments.
  • Users who also wear a WHOOP get WHOOP's own sleep performance score instead of this one — an overlapping metric trusts the more specialised band.
  • This is a reference index, not a basis for judging a sleep disorder; persistent trouble sleeping warrants a professional.

References

  1. Ohayon MM, Carskadon MA, Guilleminault C, Vitiello MV. Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: developing normative sleep values across the human lifespan. Sleep. 2004;27(7):1255-73.

    What it supports：Normative sleep duration and stage proportions by age — the reference for what stage shares are typical.

  2. Van Dongen HPA, Maislin G, Mullington JM, Dinges DF. The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation. Sleep. 2003;26(2):117-26.

    What it supports：Sleep loss accumulates in a dose-response relationship with the size of the deficit — the basis for treating sleep debt as cumulative.

  3. de Zambotti M, Cellini N, Goldstone A, Colrain IM, Baker FC. Wearable Sleep Technology in Clinical and Research Settings. Medicine & Science in Sports & Exercise. 2019;51(7):1538-57.

    What it supports：Accuracy and limits of consumer wearable sleep staging — why we weight stage shares conservatively.

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Every metric on this page is a reference index for observing your own trends. It is not medical advice and cannot replace a professional diagnosis. If you have health concerns, consult a qualified clinician.
Source module: lib/vitality/score.ts · computeSleepScore

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