Your calendar tells you how long you’ve been alive. It doesn’t tell you how well.
Biological Age does. It’s built on a foundation model trained on 2.7 million hours of nightly recordings from over 100,000 people, the largest raw-waveform bio-signal dataset assembled for this kind of work to date. That model turns your Pod’s nightly data into a number that can run younger or older than your actual years, and unlike the calendar, it moves as your habits do.
Eight Sleep developed Biological Age in collaboration with Bryan Johnson, founder of Immortals and one of the world’s most prominent voices in longevity. It updates every week. Here is what actually goes into it, how the science holds up, and how to put it to work.
The two numbers on your screen
Open the feature and you will see two figures working together.
Biological Age is your Speed of Aging translated into an age you can hold up against your calendar age. If your Pod reads 27.3 years old against a calendar age of 30, the app tells you plainly: you are reading a few years younger than your age.
Speed of Aging (sometimes called Pace of Aging) is the multiplier behind that number. It sits on a scale where 1.0x means you are aging exactly in step with the calendar. Above 1.0x, your body is aging faster than your years. Below 1.0x, slower. A 0.86x reading means your body is racking up roughly 86 days of biological wear for every 100 calendar days. Small differences in that multiplier compound into real years over time, which is exactly why the app also shows you where you land against people like you: “you’re aging slower than 91% of men in their 30s”.
Both numbers update every seven days. Neither is a verdict handed down once. They are built to move, on purpose, as your habits move.
Measured continuously from the Pod and integrations
Brings together sleep, recovery, cardiovascular, and respiratory data from your Pod, plus connected apps and health records.
Here’s the part that tends to surprise people: none of the Pod’s side of that data comes from a wearable.
Built into your Pod is a sensor that feels the tiny mechanical recoil of your body with every heartbeat and every breath, a signal called ballistocardiography, BCG for short. Think of it as your mattress noticing the faint kick your body gives each time your heart contracts. Nothing to strap on, nothing to charge before bed. You just sleep, and the Pod listens all night, isolating the signals that track most closely with aging:
- Resting heart rate
- Heart rate variability
- Breathing rate
- Sleep structure, how much time you spend in deep and REM sleep versus lighter stages
That’s the nightly, automatic layer. Connect Apple Health and, for eligible U.S. members, HealthEx, and the picture widens to your daytime activity and clinical history too, which is what turns a strong sleep-based estimate into a fuller, whole-body read (more on that below).
The science behind the science
The foundation model behind your Biological Age was pretrained on 2.7 million hours of nightly recordings from over 100,000 individuals, the largest raw-waveform biosignal pretraining corpus built for this kind of work to date.¹ That scale translated directly into performance: the resulting embeddings produced the most accurate biological age estimate yet reported for any contactless, ambient sensing method, edging out other passive approaches that try to do the same thing without a wearable.¹ From there, Eight Sleep fine-tuned the model specifically to capture how physiological patterns shift as people age, and it continues to draw on Eight Sleep’s full dataset of more than 1 billion hours of sleep data as broader context.
Instead of grading everyone against one universal definition of healthy, the model weighs three things at once: your own history and baseline, patterns from people who share your age and gender, and signals from that much larger population dataset. That combination is what makes the number personal instead of a generic scorecard.
What’s actually feeding your score
Your Biological Age breaks down into contributing factors, split into what your Pod measures directly and what you choose to connect.
Measured by your Pod, every night, automatically:
- Sleep duration, benchmarked against a goal like 8 hours
- Sleep consistency, how steady your bedtime and wake time are night to night, with a goal around 95 percent
- Deep sleep, both the raw time and the percentage of your night, since deep sleep drives most of your physical repair
- Resting heart rate, where lower generally signals a more efficient, well-recovered heart
- Heart rate variability (HRV), where a higher number relative to your peers suggests a nervous system that adapts well to stress and rest
Each factor gets a clear read: in range or out of range against your goal, with a 7-day average so one rough night does not tank the picture.
External factors, once you choose to connect them:
- Apple Health adds your daytime layer: steps and exercise minutes, checked against benchmarks like 10,000 steps a day and 150 minutes of exercise a week. This is the part your Pod literally cannot see on its own; it knows what happens in bed, not what happens at the gym.
- HealthEx, for eligible U.S. beta members, adds clinical context: glucose, cholesterol, and more, pulled from your actual medical records. This is opt-in, fully consented, and something you can disconnect at any time.
The logic is straightforward: your Pod sees the night. It cannot see your workouts, your bloodwork, or how your body is actually built. Connect more, and your estimate stops being a strong sleep-based guess and becomes