Data guide
How every Vita metric is calculated: inputs, weights, bands, limitations, and the research each rests on. Written for people who want to know why a number should be believed.
Metrics Vita computes
These numbers are ours, so the method is written out.
How stress is calculated
Stress is a 0–100 reference index where higher means more strain, combining suppressed heart rate variability (60%), elevated resting heart rate (25%) and respiratory rate (15%), all read against your own trailing 28-day baseline — a daily index, not a live reading.
See the method →How recovery is calculated
Recovery is a 0–100 reference score that compares today's HRV, resting heart rate, sleep, respiratory rate and wrist temperature against your own trailing 28-day baseline, then weights them — it measures you against your usual, not against other people.
See the method →How the sleep score is calculated
The sleep score is a 0–100 reference score combining duration (50%), deep-sleep share (25%), REM share (15%) and sleep efficiency (10%), each read against your own trailing 28-day baseline — because Apple Health gives you sleep stages but no score.
See the method →How activity load is calculated
Activity load is a 0–100 reference score for where today's expenditure sits within your own past 30 days — 70 means "heavier than about 70% of your usual days", not any absolute training standard.
See the method →How Body Age is calculated
Body Age starts from your actual age and adds or subtracts years according to how each of seven signals compares with an age-referenced value — every term is individually capped, and the result is their sum. It is a reference index, not a measurement of biological age.
See the method →Why we compare you with yourself
Vita's recovery, load and sleep scores are not compared with population norms but with your own trailing 28-day baseline, computed from the median and median absolute deviation (MAD), and requiring at least 7 days of data.
See the method →Metrics Vita reads
These come from Apple Health or your devices; Vita only reads and displays them. Here is what each one measures, what Vita does with it, and the part most easily misread.
Heart rate and rhythm metrics7
Vita reads resting heart rate, heart rate variability, daily heart-rate range, walking average heart rate, one-minute heart rate recovery and blood oxygen from Apple Health — resting heart rate and HRV being the core inputs to recovery, stress and Body Age.
Raw sleep metrics4
Apple Health provides sleep stages (core / deep / REM / awake), time in bed, sleeping wrist temperature and respiratory rate, but **no sleep score** — Vita's sleep score is computed from those raw stages.
Activity and energy metrics7
Vita reads steps, exercise minutes, stand time, active energy, basal energy, flights climbed and physical effort — the last three of which make up the activity load score.
Body composition metrics6
Weight, BMI, body fat percentage, lean body mass and body temperature mostly come from a smart scale or manual entry rather than the Apple Watch — Vita displays them and uses them as context for nutrition and lab-report interpretation.
Gait and mobility metrics7
Walking speed, step length, walking asymmetry, double support time, walking steadiness, stair speed and six-minute walk distance — Apple's mobility family, which relates to long-term functional health and fall risk, and is the group closest to “healthspan” that most people never look at.
Environment and hearing exposure2
The Apple Watch logs environmental sound exposure and the iPhone logs headphone audio exposure — hearing loss is irreversible, and these are among the few wearable metrics that can warn ahead of time.
Every metric on this page is a reference index for observing your own trends. It is not medical advice and cannot replace a professional diagnosis. If you have health concerns, consult a qualified clinician.
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