Measuring biological age: which tests actually mean something, and which don't

Your calendar age is just a number -- it tells you nothing about how healthy your cells are. Biological age says (in theory) more: it reflects how much ageing your body has genuinely accumulated. The real question is which test measures that reliably. On the Biological age & clocks topic page you will find a full overview of everything we know about ageing clocks; this article tackles the practical side: does measuring your biological age actually make sense, and if so, how do you go about it?

Epigenetic clocks measure something that matters

The most thoroughly studied method is DNA methylation testing, also known as an epigenetic clock. Among all the variants, GrimAge is the most robust: in large studies it predicts mortality better than your birth year alone. DunedinPACE, a clock that estimates the pace of ageing rather than an absolute age, shows comparable associations. Higher scores are linked to a greater risk of serious disease. That is not nothing.

At the same time, these are associations, not proven causes. Whether a lower clock age actually means you will age more healthily has not yet been demonstrated in long-term follow-up studies in humans. The measurements also do not work equally well across all cell types: blood gives different results than saliva or tissue. If you take two tests on the same day using different methods, you may well get two different answers. Large studies put the typical gap between biological and calendar age at roughly one to two years, though no study has established a firm upper limit.

Saliva tests: technically reasonable, clinically still uncertain

Home kits based on saliva are more convenient than a blood draw and technically not bad: they correlate reasonably well with calendar age and pick up biological signals drawn from research on tens of thousands of people. But there is an uncomfortable flip side. As saliva-based models get technically better at estimating your age, the link with actual health outcomes -- such as mortality -- tends to disappear. A more precise number is not automatically a more meaningful one. Treat these tests as a rough orientation, not as a statement about your life expectancy.

Commercial tests are ahead of the evidence

The technology behind DNA methylation testing has genuine scientific value, but commercial versions have not yet been independently validated. Many models underperform due to methodological shortcomings, and it remains unclear whether your score changes when you start living more healthily. Whether online tests are reliable simply cannot be determined from the available studies: independent validation studies of specific products are lacking. These tests are scientifically interesting, but as personal health tools they are premature.

That applies even more forcefully to the promise of organ ages. Blood tests can map biological ageing and flag risks associated with specific organs, but they cannot directly measure an "organ age." What you get are population averages, not a verdict on the state of your liver or your heart.

What your doctor can offer

Standard blood markers -- fasting glucose, HbA1c, LDL cholesterol, HDL cholesterol, triglycerides, blood pressure and BMI -- together give you a reliable picture of your cardiovascular and metabolic risk. They are not glamorous, but they are validated, covered by insurance, and useful for making concrete decisions. For most people, epigenetic tests are currently available mainly through scientific or medical research programmes, not as everyday consumer products. Any result always needs professional interpretation.

What your result tells you, and what it doesn't

An epigenetic clock result is most useful as one signal alongside other information about your health. Use it as a starting point for a conversation with your doctor, not as a definitive verdict. Whether you can meaningfully and lastingly lower your biological age has yet to be demonstrated. The available studies are small or conducted in mice, and there is no intervention with solid clinical backing to build on.

The honest conclusion: epigenetic clocks are the best tools we currently have for measuring biological ageing, but they are not yet a clinical decision aid. Standard blood tests at your doctor's office carry less prestige but give you more to work with.