Epigenetic clocks estimate your biological age from chemical tags on your DNA called methylation. Horvath’s clock estimates age, GrimAge estimates mortality risk, and DunedinPACE measures how fast you are aging right now. Each answers a different question, and none is a diagnosis. They are useful for tracking trends over time, but single results can vary, so interpret one number with caution.
What Is an Epigenetic Clock and How Does DNA Methylation Work?
DNA methylation means that small chemical groups attach to specific spots on your DNA, usually at sites called CpGs. Those patterns shift in predictable ways as you age. An epigenetic clock is an algorithm that weights methylation at selected sites and converts the result into a single number, typically from a blood sample.
Different clocks are trained on different goals, which is why your results can look so different from one test to the next. For background on the concept itself, see our guide to biological age.
The Horvath Clock: The First Multi-Tissue Age Predictor
Steve Horvath published his clock in 2013. He used about 8,000 samples from 51 healthy tissues and cell types to select 353 CpG sites that together predict age across most of the body. The clock reads near zero in embryonic stem cells, which fits the idea that it tracks something real about biological development.
Because it was built to match calendar age, it is a first-generation clock. It showed that methylation could act as a precise age meter. Later clocks aimed to predict health outcomes more directly.
GrimAge: A Clock Built to Predict Lifespan
GrimAge, published in 2019, took a different route. Researchers first built methylation-based estimates of seven blood proteins, including PAI-1 and GDF-15, plus smoking pack-years. They then combined these into a composite that predicts time to death. According to the GrimAge paper, it is technically a mortality risk estimator, expressed in years so that it behaves like an age.
The age-adjusted version was strongly associated with the number of age-related conditions a person had. That makes GrimAge a popular choice for studies of healthspan and lifespan. Our article on healthspan versus lifespan explains why that distinction matters.
DunedinPACE: A Speedometer for Aging
DunedinPACE asks a different question: how fast are you aging? Researchers used the Dunedin Study birth cohort, tracking 19 indicators of organ-system health across four time points over two decades. They distilled that pace of decline into a single blood test.
The resulting score was associated with illness, disability, and mortality, with effect sizes similar to GrimAge. It also showed high test-retest reliability, a major selling point. A score near 1.0 indicates aging at roughly the average pace, with lower values suggesting slower aging.
Can You Trust Your Epigenetic Age Result?
Partly. A 2022 Nature Aging study found that technical noise could make six prominent clocks differ by up to 9 years between replicates of the same sample. A redesigned approach brought most replicates within about 1.5 years, so it is worth asking any provider how it handles reliability.
In practice, this means a single reading deserves caution. Different tests use different clocks and sample types, so numbers from one provider are not comparable to another’s. Pick one test, repeat it under similar conditions, and focus on direction rather than any one result.
Can Lifestyle or Supplements Move Your Clock?
Some interventions have shown signals. In the DO-HEALTH trial of 777 older adults, 1 gram of omega-3 daily slowed three of four epigenetic clocks, including GrimAge2 and DunedinPACE, by roughly 3 to 4 months over three years. That is a small, real effect, not a reversal.
Be wary of dramatic claims. A changed clock score is a marker, not proof of longer life, a point we explore in can you actually reverse biological age.
How to Use Epigenetic Clocks in Your Longevity Plan
Treat them as one dashboard instrument among several. Pair a clock with conventional measures such as blood pressure, blood sugar, lipids, and fitness, since those have decades of evidence behind them. Retesting once or twice a year is plenty for most people, and a trend across several tests tells you far more than a single snapshot.
Most importantly, do not buy supplements based on one number. Use clock results to start a conversation with your doctor, not to replace one.
Epigenetic Clock Frequently Asked Questions
Which Epigenetic Clock Is the Most Accurate?
It depends on the question. Horvath’s clock is best known for estimating calendar age, GrimAge for predicting mortality risk, and DunedinPACE for measuring the speed of aging. For tracking change over time, reliability matters most, so stick with one consistent test.
Can Supplements Lower My Epigenetic Age?
One randomized trial found that 1 gram of omega-3 daily slowed three epigenetic clocks by a few months over three years in older adults. Evidence for most other supplements is limited, so treat claims of dramatic reversal with skepticism.
Are At-Home Epigenetic Age Tests Reliable?
Quality varies. Technical noise can shift some clock results by several years, and tests differ in which clock and sample type they use. Choosing one provider and watching trends gives you better information than a single reading.
What Is a Good DunedinPACE Score?
A score near 1.0 indicates aging at about the average pace, with lower values suggesting slower aging and higher values faster aging. Treat the number as a trend marker to discuss with your doctor, not a verdict on your health.