YOUR SLEEP TRACKER IS GUESSING. HERE’S HOW WELL.

There is a particularly modern way to ruin a perfectly decent morning: wake up feeling reasonably rested, check your sleep score and discover that apparently you slept terribly.

The number feels objective. That is its power. It is also the reason we sometimes forget what the number actually represents.

Consumer sleep wearables typically estimate sleep from combinations of movement, heart rate, heart-rate variability and other sensor signals. They can be useful for observing patterns across many nights. But estimating sleep stages from the wrist is not the same thing as measuring brain activity, eye movements and muscle tone in a clinical sleep study.

The American Academy of Sleep Medicine has warned against using consumer sleep technology as a substitute for clinical evaluation. Validation research also shows that performance varies by device, algorithm, population and sleep outcome.

This does not make the technology useless. A trend can be genuinely informative. If your sleep duration falls every week you travel, or your schedule shifts later every weekend, the device may make a pattern visible that you had not noticed.

The mistake is asking one score to answer a question it cannot fully answer: “How healthy was my sleep last night?”

A better reading combines the data with function. Are you struggling to stay awake during the day? Is insomnia persisting for weeks? Do you wake repeatedly? Has someone noticed loud snoring, choking or pauses in breathing? Those are different questions from whether Tuesday’s score was 71 or 84.

There is even a word, orthosomnia, for the pursuit of perfect sleep metrics becoming part of the sleep problem itself. You do not need to diagnose yourself with it to recognise the dynamic: more tracking can sometimes create more worry rather than more useful information.

“Use the number as a clue, not a verdict. The goal of sleep tracking is to understand your sleep better, not to become less able to know how you feel without checking an app first.”

Use the number as a clue, not a verdict. The goal of sleep tracking is to understand your sleep better, not to become less able to know how you feel without checking an app first.