Sleep quality score
What sleep quality score means, how it's calculated, and how to improve it.
More than just hours in bed
You can spend eight hours in bed and still wake up feeling terrible. That's because sleep quality isn't just about duration; it's about what happens while you sleep. The Sleep Quality score (0 to 100) captures the night itself: how long, how continuous and how deep.
Sleep researchers make the same distinction. The National Sleep Foundation's consensus on what "good sleep" means for healthy people named four measurable markers: falling asleep within about 30 minutes, waking no more than once for longer than five minutes, spending under 20 minutes awake after sleep onset, and sleeping for at least 85 % of the time in bed (Ohayon 2017). None of those is the number of hours.
What goes into the score
Seven components, six of them about last night so that a bad night shows up the same morning instead of being averaged away:
- Your device's own night score, the largest part, where the device reports one: Garmin, Withings and Oura calibrate it from raw movement and heart rate, and MyBodyAI reads it against your own 30-day average: a 72 is a good night for someone who usually reads 64 and a poor one for someone who usually reads 84
- Sleep stages: the share of deep and REM sleep against age-adjusted targets. Spending 15 to 25 % of the night in deep sleep means your body had time for serious physical repair; 20 to 25 % in REM keeps your cognitive and emotional processing on track
- Duration against your personal optimum: 7 to 9 hours is the sweet spot for most adults, though individual needs vary (Walker 2017), and the optimum adapts to what your own good weeks look like. Oversleeping costs points too
- Sleep efficiency: if you're asleep for 85 % or more of the time you spend in bed, that's healthy. Less than that often means restless nights
- Sleep onset: how long the night took to start, where the device reports it
- Overnight recharge: how much Body Battery the night restored, on watches that have it
- The last three nights, lightly weighted, so that one odd reading does not swing the whole picture
Regularity of bedtime is scored separately, in the Body Clock index, because it is a property of the week rather than of one night. It matters at least as much: in a UK Biobank analysis of 60 000 people, irregular sleep timing predicted mortality more strongly than short sleep did (Windred 2024).
What the score is not
It is not how you feel, and the two can disagree. Sleep researchers separate objective quality, the stages and continuity a recording shows, from subjective quality, the answer to "how did you sleep?" The morning feeling depends heavily on the stage you woke from, on stress and on mood; a night with excellent architecture can feel poor if the alarm landed in deep sleep. Over weeks the two converge, which is why the trend matters more than any single night.
It is also not a diagnosis. A persistently low score with loud snoring, gasping or unrefreshing sleep despite enough hours is a reason to ask a doctor about sleep apnea, which a wearable can hint at but not confirm.
What moves it, in order of size
- Alcohol: the largest single suppressor of REM and the most common cause of a fragmented second half of the night
- Timing: a bedtime that shifts by two hours between weekdays and weekends costs deep sleep on the catch-up nights and REM on the short ones
- Temperature and light: a room above about 21 °C and light during the night both reduce deep sleep
- Late caffeine and late hard training: both delay sleep onset and raise night-time heart rate
- Illness and stress: a rising overnight heart rate with more awakenings is often the first sign of either, days before symptoms
How wearables score it
Every device infers stages from movement, heart rate and HRV rather than brain waves, so the deep and REM percentages are estimates with a typical error of 20 to 30 minutes per stage against a sleep lab (Chinoy 2021). Duration and continuity are measured more reliably than stages. The practical rule: trust the device on how long and how broken your sleep was, treat the stage split as indicative, and never compare stage percentages between two brands.
Why it matters for your health
In MyBodyAI, low sleep quality doesn't just affect the Sleep Quality index; it ripples across your entire health profile. Recovery drops, Body Alert climbs, and stress resilience weakens. The good news? Even small improvements in sleep habits tend to show up in the data within a week or two, and the levers with the best evidence are collected in the sleep hygiene entry.
Frequently asked questions
What is a good sleep quality score?
In MyBodyAI, scores above 80 mean a night with enough sleep, healthy continuity and a normal share of deep and REM sleep; 60 to 80 is decent with one weak spot; below 60 usually means short or broken sleep with little deep sleep. Judge the weekly pattern, because one poor night after a late dinner is noise and five in a row is a signal.
Why do I feel tired after a night with a high score?
The score describes the recording, not the feeling. Waking from deep sleep, a stressful day ahead, dehydration or a mild illness can make a structurally good night feel poor, and the opposite happens too. If the gap persists for weeks, look at timing: sleep that is long enough but out of step with your body clock scores well on stages and still leaves you groggy.
Which matters more, sleep duration or sleep quality?
Both, and they are not independent. Below about six hours, no amount of continuity compensates; above seven hours, continuity, deep sleep and a regular schedule separate a restorative night from a merely long one. The best-supported single habit is a fixed wake time, which improves both at once.