Sleep Regularity Calculator
Score your sleep consistency — research published in 2026 shows that sleep regularity predicts cardiovascular health and quality of life better than sleep duration alone.
Regular sleep schedule calendar representing sleep consistency measurement · Photo: Unsplash
The Sleep Regularity Index — What New Research Shows
A study published in the Journal of Sleep Research in April 2026 examined 768 middle-aged to older adults and found that sleep regularity (measured by the Sleep Regularity Index) was significantly associated with physical and mental health-related quality of life — independent of total sleep duration. This adds to a growing body of evidence suggesting that when you sleep matters as much as how long you sleep. The same research group has previously shown that irregular sleep is associated with higher cardiovascular disease risk and mortality compared to consistent sleep timing, even when total hours are equivalent.
What Is the Sleep Regularity Index?
The Sleep Regularity Index (SRI) was developed by Andrew Phillips and colleagues and measures the probability that any two points in time 24 hours apart share the same sleep/wake status. An SRI of 100 means perfectly consistent sleep timing every day. An SRI of 0 means completely random, unpredictable sleep timing. Most healthy adults with regular schedules score 75–90. People with shift work, irregular schedules, or significant social jet lag often score 50–70.
The Sleep Regularity Index
The Sleep Regularity Index (SRI), developed by Andrew Phillips and colleagues at Harvard Medical School, quantifies sleep consistency as a single metric ranging from 0 (completely irregular) to 100 (perfectly regular). It captures the day-to-day consistency of the transition between sleep and wake states across all 24-hour periods, not just nighttime sleep. Research using the SRI in large longitudinal datasets has found it is one of the strongest sleep-related predictors of health outcomes -- including mental health, metabolic health, and cancer outcomes -- outperforming total sleep duration in predictive power for several outcomes.
A landmark 2023 study by Phillips et al. in Sleep Health found that higher sleep regularity was associated with significantly lower all-cause mortality and lower risk of cancer mortality, even after controlling for sleep duration. The magnitude of the relationship was comparable to the well-documented effects of sleep duration on mortality. This finding suggests that the consistency of when you sleep may be as important as how much you sleep for long-term health outcomes.
Improving Your Sleep Regularity Score
The most direct intervention for low sleep regularity is a fixed wake time maintained 7 days a week -- the single most powerful behavioral lever for improving the SRI. Wake time consistency directly controls the timing of the cortisol awakening response, morning light exposure, and adenosine clearance baseline that together determine the reliability of the entire 24-hour sleep-wake cycle. Social jet lag -- sleeping significantly later on weekends -- is the primary driver of low SRI scores in working adults. Reducing weekend sleep shift to under 60 minutes from weekday timing produces rapid and substantial SRI improvements in most people.