VITALSetting it up
To get sleep data, you need to turn on Track Sleep with Apple Watch. Apple also advises that you:
- wear your watch to bed for at least an hour each night
- charge it to at least 30% before bed, because it can’t track your sleep if the battery runs out
- wear it snugly, because a loose watch can pick up too much movement during normal sleep
The watch adds what it records to the Health app on your iPhone, where you can look back over your nights.
How the watch estimates sleep
Apple says Apple Watch uses signals from its accelerometer, the sensor that detects movement, to estimate when you’re awake and when you’re in REM, Core or Deep sleep. Apple trained and checked these models against polysomnography, the full overnight sleep study that clinicians treat as the gold standard.
A watch can’t record everything a sleep study does, so its stages are best read as a guide.
What the stages mean
Through the night you move through the stages of sleep in cycles that take around 90 minutes, and you go through them several times. Apple Watch shows four:
- Awake: times you were awake during the night.
- REM: the stage when you dream.
- Core: Apple’s name for lighter sleep.
- Deep: the deepest sleep, when you’re hardest to wake. It tends to come in the first third of the night.
You can see the time and percentage you spent in each stage.
Sleep Score and other readings
Each morning after you wake, Apple Watch gives you a Sleep Score from 0 to 100. Apple says it’s based on how long you slept (50 points), how consistent your bedtime has been over the last 13 nights (30 points) and interruptions during the night (20 points).
Apple Watch can also track your breathing rate as you sleep, and newer models can show changes in your overnight wrist temperature.
How accurate is it
Apple says Apple Watch is not a medical device, and that its breathing rate readings aren’t intended for medical diagnosis. Fit, battery and wearing it all night all make a difference to what it records. It’s more useful to look at your sleep over a week or more than to read too much into one night’s stages.
How much sleep you need
The NHS says adults need 7 to 9 hours of sleep. If you’ve had trouble sleeping for months, if changing your sleep habits hasn’t helped, or if poor sleep is making daily life hard to cope with, the NHS suggests seeing a GP.
In Vital
Vital doesn’t track sleep itself. With your permission, the Sleep page reads what your watch saves to Apple Health. It shows your time asleep against a target of 7 hours 30 minutes, the night’s stages (Awake, REM, Core and Deep) and, when your watch records them, your overnight heart rate, HRV, breathing rate and blood oxygen. It also shows your sleep debt over the past week and your usual bedtime and wake time. Last night’s sleep is one of the two readings the Readiness card waits for each morning.
Vital for iPhone shows last night’s sleep from Apple Health right next to your readiness.
Get Vital for iPhoneVital gives general information about fitness and wellbeing. It is not medical advice, and it does not diagnose or treat any condition.