Sleep scores: what to trust and what to ignore

The score is a summary, not the night itself

A sleep score combines measurements and assumptions chosen by the app. Two apps can give different scores for the same night because they weight duration, timing, movement and other signals differently.

Consumer trackers infer sleep from signals such as movement and heart rate. A sleep laboratory also measures brain activity and other physiological signals. A tidy percentage on a wrist is not the same kind of measurement.

Look for a pattern you can act on

Use a week of bedtime, wake time, estimated sleep and how alert you feel during the day. If the score drops, first check whether the device recorded the night properly. Then ask whether the change repeats.

Being awake but still can be difficult for a tracker to recognise. Avoid deciding that you slept well solely because the app reports it, or that you slept badly solely because the score fell.

Keep the useful signals in perspective

Make one change and keep a short note

Choose a consistent wake time, protect a wind-down period or reduce late caffeine if it seems relevant. Record the change and your daytime alertness; an improved score alone does not show what caused it.

Ask a health professional about persistent sleep problems, disruptive snoring or excessive daytime sleepiness. A simple sleep diary can help explain the problem better than a single score.