Epigenetic Clocks and Biological Age Testing

GRADE 3·MIXED(3 of 5)Evidence grade 3 of 5, Mixed. Read how the Atlas grades evidence.

The underlying science is published and peer-reviewed with reproducible group-level associations to mortality and disease, but individual-level accuracy, cross-clock consistency, and clinical actionability are not yet established, and no consumer product is FDA-cleared as diagnostic.

Reference only. Not medical advice.

Epigenetic clocks are statistical models that estimate a person's biological age from patterns of DNA methylation, a chemical modification of DNA that changes in predictable ways over the lifespan. First-generation clocks (Horvath, Hannum) were trained to predict chronological age and achieve strong correlation with actual age, with median errors of roughly three to five years in the original validation cohorts. Second-generation clocks such as PhenoAge and GrimAge were instead trained against clinical biomarkers, smoking history, and mortality data, and have shown better ability to predict future disease and death risk in longitudinal cohort studies. DunedinPACE, built from a New Zealand birth cohort followed for decades, estimates the current pace of biological aging rather than a fixed age. Validation work is active and mixed. A 2025 study in Nature Communications compared fourteen widely used clocks against 174 incident disease outcomes and all-cause mortality in nearly 19,000 adults and found meaningful differences in performance between clocks, meaning results are not interchangeable across products. Known limitations include training-data bias toward European-ancestry cohorts, technical noise and low reproducibility on commercial methylation arrays, systematic error at older ages, weak and inconsistent associations with individual lifestyle changes over short time periods, and uncertainty about whether the specific CpG sites used are causally linked to aging or are simply correlated markers. Commercially, direct-to-consumer tests from companies including TruDiagnostic, Elysium Health, and others report a "biological age" number to consumers, typically for several hundred dollars. These tests run on CLIA-certified laboratory infrastructure but are marketed as wellness or informational products rather than diagnostic tests, and none has received FDA clearance, approval, or de novo authorization as a medical diagnostic. Companies state, and regulators require, that results should not be used to diagnose, treat, or prevent disease. The scientific consensus is that epigenetic clocks are a legitimate and rapidly developing research tool for population-level aging research and clinical trial endpoints, but that individual-level predictive precision, actionability, and cross-clock comparability remain unresolved, making single-number consumer "biological age" scores a commercial extrapolation ahead of full clinical validation.

Epigenetic clocks are statistical models that estimate a person's biological age from patterns of DNA methylation, a chemical modification of DNA that changes in predictable ways over the lifespan.