Ask anyone how much sleep they should get and you will hear the same number: eight hours. It is one of the most repeated health rules in existence. It is also not what the scientific consensus actually says.
What the consensus recommendation is
In 2015, the American Academy of Sleep Medicine and the Sleep Research Society published a joint consensus statement on sleep for healthy adults. Their recommendation: 7 or more hours per night on a regular basis (Journal of Clinical Sleep Medicine, 2015).
Seven is the floor of the recommended range, not a ceiling, and some people genuinely need more. But the difference between “7 or more” and “8” matters a great deal when a number becomes a target that software scores you against.
Why the difference matters for a readiness score
We learned this the practical way. An early version of Readiness Coach scored sleep duration against an 8-hour target. The result: users sleeping 7 hours and 15 minutes, comfortably inside the consensus recommendation, woke up to a sleep score that quietly told them they were falling short. Every morning. That is not science; that is nagging.
The current model scores duration against a 7-hour target, aligned with the AASM consensus. Sleep at or above 7 hours earns full duration credit. Below it, the score falls in proportion. The rest of the sleep component looks at deep sleep, REM and efficiency where your device reports them, and the full model is public if you want the weights.
Duration is not the whole story
Two nights of identical length can produce very different recoveries, and the research gives at least one everyday reason: alcohol. A prospective observational study of nocturnal physiology found that evening drinking measurably raises overnight resting heart rate (Nutrients, 2025), which is one reason a “full night’s sleep” after a late dinner party can still leave your recovery metrics flat.
This is why sleep is 40% of our readiness score rather than all of it. Overnight HRV and resting heart rate carry the recovery story that duration alone misses. If your watch keeps HRV to itself, as Garmin does on iOS, there is a two-tap fix for that.
The practical takeaways
- Aim for 7 or more hours, per the actual consensus, and stop treating 8 as a pass mark you keep failing.
- Judge sleep by trend, not by single nights. One short night moves tomorrow; a short week moves your baseline.
- If your recovery metrics look worse than your sleep duration suggests, look at what happened before bed, with alcohol as the best-documented everyday suspect.
Readiness Coach reads your sleep and heart rate from Apple Health and folds them into one morning score, calibrated to your own baselines. It is a general wellness app, not a medical device, and it does not diagnose or treat anything.