A user sleeps 8 hours. Sounds healthy. But those 8 hours started at 2am — three hours later than usual — after a week of sleeping 6 hours a night. They’ve accumulated over 10 hours of sleep debt, their circadian rhythm is disrupted, and their body hasn’t had enough consistent deep sleep to properly recover. The duration looks fine. The sleep health doesn’t.
The Sleep Score captures this full picture. It measures sleep health across seven factors that go well beyond hours logged — consistency, timing, accumulated debt, and how well the body actually recovers during sleep. Each factor is independently scored from 0 to 100 with its own sub-score and state, so the overall number always explains why sleep was good or poor and which specific dimension needs attention.
Four factors work from phone data alone. Three require a wearable. The phone factors capture behavioral dimensions (when you sleep, how much, how consistently, whether you’re accumulating debt), while the wearable factors capture physiological recovery (deep sleep, REM sleep, sleep continuity). The behavioral factors happen to be the most actionable — they’re the ones users can directly change.
| State | What It Means |
|---|---|
| High (80–100) | Consistent, well-timed sleep with adequate duration and recovery |
| Medium (60–79) | Decent sleep overall, but regularity, debt, or recovery could improve |
| Low (40–59) | Sleep is likely affecting daytime function — timing, debt, or quality is off |
| Minimal (0–39) | Significant sleep deficit — duration, consistency, or recovery is critically low |
Science: Every factor in the Sleep Score is grounded in peer-reviewed research. For the evidence behind each one, see The Science Behind the Sleep Score.
Sleep Score Factors
The Sleep Score is built from seven factors. Each returns a value (what was measured), a sub-score (0 to 100), a state (minimal, low, medium, high), and a goal (a static, evidence-based target).
Sleep Duration
Total time spent asleep during the night. The foundation of sleep health — chronic short sleep is one of the strongest predictors of long-term health decline, increasing risk for cardiovascular disease, metabolic disorders, and cognitive impairment. But duration alone says little about quality. Eight hours of fragmented, poorly timed sleep doesn’t produce the same recovery as seven and a half hours of consistent, well-timed sleep. That’s why duration is one factor among seven, not the whole score.
Goal: 8 hours (480 minutes) | Phone
Sleep Regularity
Consistency of bed and wake times across days. This is often the most underrated sleep factor — and one of the most impactful. Research shows that irregular sleep timing is independently associated with higher mortality risk, even after controlling for duration. Someone sleeping 7 hours at the same time every night may have better health outcomes than someone sleeping 8 hours on an erratic schedule. The body’s internal clock depends on timing consistency to regulate hormones, metabolism, and recovery cycles. Going to bed and waking up at roughly the same time — including weekends — is one of the most powerful sleep habits a person can build.
Goal: 100 (consistency index) | Phone
Sleep Debt
Accumulated shortfall between sleep need and sleep obtained over time. Sleep debt doesn’t reset after one good night — it accumulates and takes several nights of adequate sleep to clear. A user sleeping 6 hours when they need 8 builds 2 hours of debt per night. After five days, that’s 10 hours of debt that affects cognitive performance, mood, and physical recovery. This is why the Sleep Score can remain moderate even after a single long night of sleep — the debt factor remembers the accumulated deficit.
Goal: 0 hours | Phone
Circadian Alignment
How well sleep timing matches the body’s internal clock. Sleeping at irregular times or significantly outside one’s natural circadian window disrupts hormone regulation, metabolism, and cognitive function. This factor captures the difference between sleeping at a consistent, appropriate time and sleeping at erratic or shifted hours. Morning light exposure is one of the strongest natural anchors for circadian rhythm — it’s the simplest intervention for users whose alignment is low.
Goal: within 30 minutes of optimal timing | Phone
Sleep Continuity
How uninterrupted sleep is, measured by awakenings and restlessness during the night. Frequent disruptions prevent the body from completing full sleep cycles, reducing time spent in the restorative stages (deep sleep and REM) even when total duration is adequate. Environmental factors — noise, light, temperature, a partner’s movement — are the most common causes. A user who sleeps 8 hours but wakes four times may get less restorative sleep than someone who sleeps 7 hours uninterrupted.
Goal: 0 disruptions | Wearable
Physical Recovery
Duration and timing of deep sleep (slow-wave sleep). Deep sleep is when the body does its most intensive physical repair — tissue growth, muscle recovery, immune system strengthening. The amount of deep sleep naturally decreases with age and is reduced by alcohol, late intense exercise, and irregular sleep timing. This factor tells your product whether a user’s body is getting the physical recovery it needs, regardless of total hours slept.
Goal: 90 minutes | Wearable
Mental Recovery
Duration and timing of REM sleep. REM sleep is critical for cognitive function — memory consolidation, emotional regulation, and creative problem-solving. REM periods get longer in the later sleep cycles, which means cutting sleep short disproportionately reduces REM time. A user who consistently sleeps 6 hours may be getting adequate deep sleep but significantly less REM than their brain needs. This factor makes that distinction visible.
Goal: 120 minutes | Wearable
How Factors Interact
Sleep factors cluster into two natural groups, and the interactions within and between them tell the real story.
The behavioral cluster (phone). Duration, regularity, debt, and circadian alignment are all interconnected. Irregular sleep timing makes it harder to get adequate duration, which builds debt, which further disrupts circadian alignment. The cycle compounds — and it works in reverse too. Improving regularity (one habit change) often cascades into better duration, lower debt, and improved alignment without the user consciously targeting each factor.
The recovery cluster (wearable). Continuity, physical recovery, and mental recovery depend on each other. Disrupted sleep fragments the sleep cycles that produce deep and REM sleep. A user can spend 8 hours in bed but get minimal deep sleep if they wake frequently. These factors tell your product whether the body and brain are actually recovering, not just whether the user was in bed long enough.
Cross-cluster effects. The behavioral factors set the stage for recovery. Poor regularity and circadian misalignment reduce the body’s ability to achieve deep sleep even when continuity is good. A user who sleeps at erratic times may see low physical and mental recovery scores despite sleeping long enough and without interruptions — the timing itself disrupts the sleep architecture.
When your product reads the factor breakdown, the behavioral factors are the levers. They’re what users can change, and improving them tends to lift the recovery factors as a secondary effect.
Pairing with Readiness
The Sleep Score and Readiness Score are closely related but measure different things. Sleep measures how well the user slept. Readiness measures how recovered the user is — which depends on sleep but also factors in accumulated physical strain and cardiovascular signals.
A user can have a good Sleep Score but low Readiness if they’ve been under heavy physical strain for several days. Conversely, readiness can recover faster than sleep debt clears if the most recent night was excellent. Using both scores together gives a more complete picture than either alone.
Factor-to-Habit Guide
When a factor scores low, your product can surface a targeted, sustainable habit. Sleep habits are especially effective when they’re small and consistent — sleep responds better to routine than to dramatic one-time changes.
| Factor | When Low, Suggest… |
|---|---|
| Sleep Duration | ”Try going to bed 20 minutes earlier this week” — small, incremental shifts stick better than dramatic changes |
| Sleep Regularity | ”Keep your wake time within 30 minutes of the same time every day, including weekends” — regularity starts with wake time, not bedtime |
| Sleep Debt | ”You’ve built up some sleep debt — add 20-30 minutes of extra sleep over the next few nights” — debt clears gradually, not in one night |
| Circadian Alignment | ”Get natural light within 30 minutes of waking” — the strongest natural circadian anchor |
| Sleep Continuity | ”Check your sleep environment — dark, cool, and quiet makes a measurable difference” — the most common disruption causes are environmental |
| Physical Recovery | ”Avoid intense exercise within 2-3 hours of bedtime” — late exertion suppresses deep sleep |
| Mental Recovery | ”Avoid cutting sleep short — REM periods are longest in the final sleep cycles” — the last 1-2 hours of sleep are disproportionately REM-rich |
Product tip: Sleep habits build slowly. The most effective recommendations are ones users can maintain for weeks, not heroic one-night efforts. Frame guidance around consistency — “try this for a week” rather than “do this tonight.”
Phone vs Wearable
The Sleep Score works with phone data alone — four of seven factors are available without a wearable. These four (duration, regularity, debt, circadian alignment) cover the behavioral dimensions of sleep: when and how consistently a user sleeps, and whether they’re accumulating a deficit. These are also the most actionable factors — users can directly change their sleep timing and consistency.
Wearable data adds the recovery layer: sleep continuity (how uninterrupted sleep is), physical recovery (deep sleep), and mental recovery (REM sleep). These factors reveal whether the body and brain are actually recovering during sleep, not just whether the user was in bed long enough. Heart rate and motion data during sleep enable this analysis.
A common product pattern: launch with phone data to maximize user reach and surface the behavioral factors users can act on immediately. Then prompt engaged users to connect a wearable for deeper recovery insights — “Want to see how well your body is actually recovering? Connect a wearable for your full sleep breakdown.”
Further Reading
- The Science Behind the Sleep Score — peer-reviewed evidence for each contributing factor
- What are Health Scores and Score Factors — foundational guide to the scoring model
- Sleep Score — Docs — API reference, schemas, permissions, and integration details
- Readiness Score Explained — recovery and strain scoring that builds on sleep data
- Wellbeing Score Explained — holistic health score that includes sleep factors