the numbers, in plain words
by Aman Priyadarshi · september 12, 2026
Short explainers for the readings RestUp gives you. Each one defines the term first, then says how RestUp calculates it, then what it can and cannot tell you.
- How the readiness score worksThe five things RestUp weighs each morning, how each is compared with your own baseline, and what the bands mean.
- Sleep debt, explainedWhat sleep debt is, how RestUp counts it against the target you set, and why a lie-in repays only part of it.
- Chronotype: lion, bear, wolf or dolphinHow your body's preferred sleep window is read from real nights instead of a quiz, and what social jet lag means.
- HRV against your own baselineWhy a single HRV number means little, what a personal baseline is, and what being below it does and does not mean.
- Apple Watch now has a Readiness score. Do you still need an app?What Apple's built-in feature shows, which watches get it, and where a third-party app still earns its place.
- Readiness on Android, from Health ConnectWhat Health Connect provides, which watches and bands feed it, and what differs from the iPhone version.
Where to start
If readiness scores are new to you, start with how the readiness score works. It defines every component, weight and threshold the other guides refer to, so the rest read faster afterwards.
If you own an Apple Watch Series 12 or Ultra 4, read the Apple Watch Readiness guide first: Apple’s own score may be all you need. If you use Android, the Health Connect guide shows which watches give a complete reading and which leave gaps.