Epigenetic Clocks: Measuring Age from DNA

By Longevity Lab · Published: July 21, 2026

Based on peer-reviewed research — full source list at the end of this article. This is educational information, not medical advice.

What epigenetic clocks are

Epigenetic clocks estimate a person’s age from the pattern of DNA methylation — chemical groups attached to specific points in the genome that switch genes on and off without altering the DNA sequence itself. That pattern changes in predictable ways as we age, and it turned out that reading the state of a few hundred specific sites predicts age with high accuracy; the statistical models that do this are what researchers call epigenetic clocks. The yardstick every one of them is measured against is Chronological age, the plain count of years since birth. For the wider context, we have a primer on what biological age is. Methylation is not the only molecular clock in the cell either: the protective DNA caps at the ends of chromosomes tell a parallel story, set out in Genetic age and telomeres.

First and second generation

The clocks arrived in two waves:

• First generation — Horvath (2013) and Hannum (2013). Both were trained to predict chronological age, and both do it very accurately. The Horvath clock works across many tissues at once.
• Second generation — GrimAge and DunedinPACE. These were trained to predict not years but mortality risk and the pace of aging. They track real-world health and outcomes more closely — the mortality-oriented model is defined in GrimAge — the epigenetic clock of mortality.

How far you can trust them

Several caveats matter:

• Different clocks return different numbers. They were trained on different targets, so comparing one clock’s result head-to-head with another’s is not valid.
• The trend matters more than any single figure: repeat measurements with the same method tell you more than one reading.
• It is an estimate, not a diagnosis. A clock does not replace a medical workup and does not point to a specific disease.

Can you turn the clock back?

Preliminary data show that a healthy lifestyle is associated with younger readings, and a few small studies found that interventions — combined protocols, for example — slightly lowered epigenetic age. But these are small, early trials, and it is too soon to draw loud conclusions from them. The things that reliably move the markers are the same basics as always: movement, sleep, diet, and not smoking.

Availability

Commercial epigenetic age tests exist, but they are expensive and their practical value for a healthy person is limited: the result is interesting, yet it does not change the basic recommendations. For most people it is more useful, and much cheaper, to keep an eye on ordinary markers — blood pressure, glucose, lipids — and on lifestyle. Those same routine labs already feed the PhenoAge Calculator — biological age from a blood test, and anyone weighing up the options before paying for a kit can see how the approaches differ in Biological age tests: what to measure and how to choose a method.

Frequently asked questions

Sources

Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.