How old is your body really?

PhenoAge is a biological age estimation algorithm published by Morgan Levine et al. in 2018 in the journal Aging. It was developed using NHANES III data (N=9,926) and validated in NHANES IV (N=6,209). The algorithm uses nine clinical biomarkers plus chronological age to compute a composite biological age score that predicts mortality, morbidity, and physical functioning more accurately than chronological age alone. This calculator adapts the framework by mapping lifestyle factors to their known effects on those biomarkers.

A lifestyle-based biological age calculator provides a population-level estimate, not a clinical measurement. The factor weights used here are derived from large epidemiological studies (UK Biobank N=502,489, NHANES N=30,000+) and correlate strongly with clinically measured biological age markers at the group level. Individual accuracy varies because the calculator cannot account for genetics, existing medical conditions, or medication use. Think of it as a well-informed directional signal, accurate to within 2 to 4 years for most people.

UK Biobank analyses show men tend to have slightly higher rates of biological age acceleration than women at the same chronological age, with an average gap of 1 to 2 years. However, this gap is almost entirely explained by lifestyle differences: men are more likely to smoke, drink heavily, and have higher BMI. When lifestyle factors are controlled, the sex-based difference shrinks to under 0.5 years. This calculator adjusts the population comparison by sex so your percentile reflects where you sit among people of the same sex and similar age.

The Dunedin Study (Belsky et al. 2015, PNAS) tracked 954 individuals from birth and found measurable differences in biological aging rates as early as age 26. By age 38, participants showed biological ages ranging from 28 to 61, a 33-year spread within a single birth cohort. UK Biobank data shows standard deviation of biological age gap increases from approximately 3 years in the 30 to 40 age group to approximately 6 years in the 60 to 70 age group. Lifestyle choices compound over time.

Clinical biological age tests (epigenetic, blood-based) range from $199 to $499 per test. For someone who has already optimised major lifestyle factors, a clinical test can reveal whether genetic or environmental factors are creating a gap that lifestyle alone cannot close. For someone who is sedentary, sleep-deprived, or a current smoker, a lifestyle-based estimate like this calculator provides nearly as much actionable information at no cost. Clinical testing is most valuable as a tracking tool over time, measuring whether interventions are working at the cellular level.

Bryan Johnson, a tech entrepreneur, gained widespread attention from 2023 onward for his "Blueprint" longevity protocol, which involves spending approximately $2 million per year on interventions designed to minimise his biological age. His publicised results brought the concept of biological age into mainstream conversation. While Johnson's protocol involves dozens of supplements, strict dietary regimens, and medical monitoring that are impractical for most people, the underlying science he references (PhenoAge, epigenetic clocks, UK Biobank data) is the same research used in this calculator. Longevity researchers consistently find that 80 to 90% of the biological age benefit comes from basic lifestyle factors (exercise, sleep, not smoking, healthy weight) that cost nothing, not from the expensive interventions that generate headlines.

Biological age divergence begins earlier than most people expect. The Dunedin Study (Belsky et al. 2015, PNAS), which tracked 954 individuals from birth, found measurable differences in biological aging rates as early as age 26. By age 38, participants showed biological ages ranging from 28 to 61, a 33-year spread within a single birth cohort. UK Biobank data shows the standard deviation of biological age gap increases from approximately 3 years in the 30 to 40 age group to approximately 6 years in the 60 to 70 age group. This means lifestyle choices compound over time: a 25-year-old who starts exercising and sleeping well may accumulate a 5 to 8 year biological advantage over a sedentary peer by age 45.

Epigenetic age is one specific method of measuring biological age, not a synonym for it. Biological age is the broader concept referring to how old your body functions compared to population norms. Epigenetic age specifically measures patterns of DNA methylation, chemical modifications to DNA that change predictably with aging, using algorithms called "epigenetic clocks" (Horvath 2013, Hannum 2013). PhenoAge (Levine 2018) is a hybrid approach that uses clinical biomarkers rather than direct DNA methylation measurement but correlates strongly with epigenetic clocks. Other biological age measures include telomere length, composite biomarker indices, and functional assessments such as grip strength, walking speed, and cognitive tests. The lifestyle-based estimate in this calculator is calibrated against PhenoAge norms, which predict health outcomes more accurately than epigenetic clocks alone in several validation studies.