What an epigenetic clock is
An epigenetic clock is a statistical model that estimates age from DNA methylation — chemical tags on DNA that change in predictable ways over the lifespan. By measuring methylation at hundreds of sites, the clock outputs an estimated biological age that can differ from chronological age.
Why it matters for longevity
The gap between biological and chronological age (“age acceleration”) is associated with mortality and disease risk in large cohorts, which makes epigenetic clocks a leading candidate biomarker of aging — a way to measure whether an intervention is actually slowing ageing.
What the evidence shows
First-generation clocks (e.g. the 2013 Horvath clock) predict chronological age remarkably well; later “second-generation” clocks were trained to predict health outcomes. However, a 2025 head-to-head comparison of 14 clocks against 174 disease outcomes showed they vary widely and are sensitive to technical noise. They are valuable for population research but are not yet reliable enough to diagnose, or to track one person’s response to a therapy, on their own.
What to ask before testing
A single clock reading carries wide measurement uncertainty. Treat consumer “biological age” results as exploratory, look at trends rather than one-off numbers, and don’t make medical decisions on a clock value alone.