In short
Biological age estimates how worn your physiology is, as distinct from how long you have been alive. It is measured with epigenetic clocks, composite biomarker panels, or lifestyle proxies. The best clocks predict mortality and disease risk better than chronological age does. They also disagree with each other, which tells you something about how young this field still is.
Two people turn fifty on the same day. One runs half marathons, sleeps eight hours and has the inflammatory profile of a thirty-eight year old. The other has been sedentary for twenty years and carries markers typical of someone in their sixties. Chronological age cannot see that difference. Biological age is the attempt to measure it.
The three ways biological age gets measured
Epigenetic clocks
These are the most discussed and, in research settings, the most powerful. They read DNA methylation, the pattern of methyl groups attached to cytosine bases across the genome. Methylation at particular sites changes with age in ways regular enough to be modelled.
The important thing for anyone reading a marketing page is that there is not one clock. There are several, they were trained on different outcomes, and they give different answers on the same sample.
| Clock | Trained to predict | What it is good at |
|---|---|---|
| Horvath (2013) | Chronological age across many tissue types | Accuracy against calendar age; less sensitive to health status |
| Hannum (2013) | Chronological age in blood | Blood-specific accuracy |
| PhenoAge (2018) | A composite clinical phenotype of ageing | Predicting mortality and disease risk, not calendar age |
| GrimAge (2019) | Time to death, incorporating smoking history | Strongest mortality prediction of the widely used clocks |
| DunedinPACE (2022) | Rate of ageing, not accumulated age | Measuring how fast you are ageing right now |
A clock trained to predict calendar age and a clock trained to predict mortality are answering different questions. When a consumer test reports your biological age, the useful follow-up is which clock it used.
Composite biomarker panels
These combine standard clinical measurements into a single ageing index. Levine's PhenoAge algorithm, for example, uses nine routine markers: albumin, creatinine, glucose, C-reactive protein, lymphocyte percentage, mean cell volume, red cell distribution width, alkaline phosphatase and white cell count.
The practical advantage is real. These are numbers your doctor can already order, they cost a fraction of a methylation test, and they are interpretable, because you can see which individual marker is out of range.
Lifestyle proxy models
The weakest of the three and the most accessible. These estimate biological age from questionnaire inputs like activity, sleep, smoking and body composition, using weights drawn from cohort research. They cannot measure your biology, only infer from behaviours known to correlate with it. Our biological age estimator is one of these, and it publishes its full weighting table for exactly that reason.
What biological age actually predicts
This is the part that justifies the interest. Across large cohorts, epigenetic age acceleration, meaning your measured biological age minus your chronological age, is associated with all-cause mortality, cardiovascular disease, some cancers, and physical and cognitive decline. Several clocks predict these outcomes better than calendar age.
That is a meaningful finding. Somebody whose measured age runs five years ahead of their calendar age is, on population average, carrying elevated risk.
Where the science is genuinely unsettled
- Whether clocks measure cause or consequence. Methylation changes track ageing. Whether they drive it, or record it, is not resolved.
- Test-retest reliability. Run the same sample twice and results can differ by more than most providers disclose.
- Clock disagreement. Different clocks on the same sample can disagree by several years.
- Whether improving a clock improves health. The critical open question. Interventions can shift a clock reading. Nobody has shown that shifting the reading changes the outcome the clock predicts.
Why that last point matters commercially. A great deal of longevity marketing depends on the unstated assumption that lowering a clock number produces a health benefit. That assumption is plausible and it is currently unproven. Keep it in view when you are reading a sales page, including ours.
Where AKG enters the picture
The mechanistic link between alpha-ketoglutarate and epigenetic age is not arbitrary. AKG is a required cofactor for the TET family of enzymes, which participate in DNA demethylation. Since epigenetic clocks read methylation, a cofactor for the enzymes that edit methylation is a reasonable candidate to investigate.
Reasonable candidate is exactly the right strength of claim. For the full picture of what has and has not been demonstrated in humans, read our explainer on alpha-ketoglutarate.
Common questions
What is a good biological age result?
Lower than your chronological age is generally favourable, but the more useful reading is the direction over time on the same test. A single result from one clock on one sample carries more measurement noise than most people assume.
Which biological age test is most accurate?
It depends what you want accuracy about. GrimAge and DunedinPACE have the strongest published performance for health outcome prediction. Horvath is more accurate against calendar age but less informative about health. For most people a standard blood panel interpreted by a doctor delivers more actionable information per dollar than a consumer methylation test.
Can biological age be lowered?
Measured markers can improve, and interventions in fitness, body composition, sleep and smoking status have been associated with improvement. Whether that constitutes reversal of underlying biological ageing is a separate and unresolved question.
How often should I test?
No more than annually for methylation testing. The clocks move slowly and test-retest variability means shorter intervals mostly measure noise. Blood panels every six to twelve months are more informative for tracking change.