My Bio Age
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Methods & Sources

Updated

My Bio Age turns available Apple Health data into the weekly MyBioAge Index™, an age-scaled wellness estimate, alongside daily scores and metric trends. This page explains what contributes to the Index, how the time windows work, and what the results can and cannot tell you. Calculations run on your iPhone.

How the weekly Index is built

The Index uses complete Monday-to-Sunday weeks, with up to 24 weeks of history where data is available. It does not score the current incomplete week. Weekly summaries reduce the influence of an isolated daily reading; a change in today's metric does not necessarily change the latest Index.

  1. Read permitted data. My Bio Age reads the Health categories you allow and builds summaries appropriate to each metric. For example, HRV SDNN readings are grouped into daily median values, while sleep uses recorded asleep intervals with overlaps merged.
  2. Build weekly inputs. Available readings are aggregated for each complete week. Some gaps can use a recent earlier reading with reduced confidence. A week without sufficient usable data is not equivalent to a week of zero values.
  3. Put inputs into context. Applicable metrics are compared with age- and sex-specific reference values. Other inputs use the app's metric-specific calculations. The Index is not a comparison of every metric against a personal six-month baseline.
  4. Combine available signals. Standardized values are weighted by the scoring model and data confidence, then translated into an age offset from chronological age. This produces the displayed wellness estimate, not a direct measurement of cellular aging.

Which inputs contribute?

The Index model includes 12 core inputs. Some are read from Apple Health; others, such as Recovery Capacity and Training Load, are derived by the app from available health signals.

  • Cardio fitness (VO₂ max)
  • Heart rate variability (SDNN)
  • Recovery Capacity
  • Sleep duration
  • Respiratory rate
  • Resting heart rate
  • Active energy
  • Walking heart rate
  • Sleeping wrist temperature
  • Blood oxygen (SpO₂)
  • Sleep Regularity Index
  • Training Load

Systolic and diastolic blood pressure are two additional optional inputs when usable Health readings are available. Body composition can provide additional context for selected calculations. Availability depends on your devices, recorded history, and permissions; every user will not have every input. The app does not measure blood pressure from the watch itself.

For one line on each input and daily score, with a guide to each, see what My Bio Age tracks.

Daily scores and longer trends

Recovery Capacity and Training Load have their own daily views, while their historical values also contribute to the weekly Index. Stress Resilience and Circadian Alignment are separate wellness scores; they are not direct inputs to the Index. Circadian Alignment looks at available sleep and timing signals, rather than directly measuring your biological clock.

Pace of Aging describes the trend in stored weekly Index values. It does not establish the rate at which your cells age, predict lifespan, or show that a habit has reversed aging. Explore the Recovery & Strain dashboard for the distinction between daily scores and weekly trends.

Confidence, missing data, and limitations

Confidence reflects the available data and the model's coverage rules. A high-confidence label is not a clinically measured probability that the age estimate is correct. Missing or stale critical inputs can leave the Index marked Limited, with a checklist explaining coverage gaps. Follow our Apple Health data checklist if expected readings are absent.

Apple Watch cardio fitness is an estimate from eligible outdoor workouts. Wearable measurements, reference populations, and the app's own model each have limitations. Medication, illness, pregnancy, and individual physiology may affect interpretation. Pacemaker and pregnancy settings change selected calculations; they do not make the app a medical assessment.

MyBioAge Index™ is a wellness estimate based on fitness and recovery data. It is not a diagnosis, a laboratory biological-age test, or a substitute for professional medical advice. Discuss health concerns and treatment decisions with a qualified healthcare professional.

References

These sources explain underlying measurements and population reference standards. The FRIEND papers describe exercise-test reference data, and Apple's paper evaluates its cardio-fitness estimate. They do not clinically validate the combined MyBioAge Index™ or prove that changing it changes health outcomes.

Explore the method with your own data

Download My Bio Age free on the App Store to review your weekly MyBioAge Index™ and the available trends behind it. The app is completely free, with no subscription or in-app purchases. Calculations and optional AI Coach answers run entirely on your iPhone, keeping your health data private.