Hi ,

How well did you sleep last night? Do you feel rested when you wake up? And just as importantly, do you go to bed and wake up at roughly the same time each day?

In recent years, sleep science has begun to pay closer attention to something often overlooked: sleep timing regularity. One of the most robust ways to measure it is through something called the Sleep Regularity Index (SRI).

Why Sleep Regularity Matters

Multiple studies suggest that how consistent your sleep and wake times are throughout the week may be just as important as sleep quantity or quality. When sleep schedules are erratic, the body struggles to maintain internal synchrony. This can disrupt:

• Circadian alignment – leading to hormonal imbalances, poor glucose control, and weakened immunity
• Mental health – with higher risks of anxiety, depression, and mood instability
• Cognitive function – including memory, focus, and daytime alertness
• Cardiometabolic health – increasing your risk for high blood pressure, weight gain, and type 2 diabetes
• Academic and work performance, particularly in young adults.

What Is the Sleep Regularity Index (SRI)?

The SRI quantifies how predictable your sleep-wake schedule is. It measures the likelihood that you’re in the same state (asleep or awake) at any given time 24 hours apart.

• A perfect score of 100 means you’re sleeping and waking at the same times daily.
• A score closer to 0 reflects erratic patterns, with little day-to-day consistency.

How Can You Measure SRI?

Wearable devices such as Oura or WHOOP offer insights to SRI. (I haven't used either of those.) Fitbit and Apple Watch do not provide a direct SRI score. Calculating a true SRI typically requires multiple days of detailed data and complex calculations.

What If You Can’t Measure SRI easily?

Even without a device or app, you can take practical steps to support your sleep regularity. One simple habit is to wake up at the same time every day, including weekends, within a 30-minute window. Manually tracking your wake and sleep times in a notebook, calendar, or spreadsheet over 1–2 weeks can help you identify your patterns. The more regular your routine becomes, the closer your SRI will move toward optimal. And the benefits? Better mood, improved energy, and long-term protection for your heart, brain and metabolism.

I’d Love to Hear From You

Have you ever tried tracking your bedtime and wake-up times? If you’re not a shift worker and still find it hard to keep a regular schedule, what gets in your way? Is it work demands, screen time, social commitments, or something else entirely?

Reply to this email. I’d love to learn more about what helps or hinders your sleep rhythm.

To better sleep and better health,

Shabnam

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References

1. Phillips, Andrew JK, et al. "Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing." Scientific reports 7.1 (2017): 3216.
2. Lunsford-Avery, Jessica R., et al. "Validation of the sleep regularity index in older adults and associations with cardiometabolic risk." Scientific reports 8.1 (2018): 14158.

Dr. Shabnam Das Kar, MD

Functional Medicine Doctor

Tiny Habits Coach

Email: info@drkarmd.com