You have two ages. Only one of them matters

My chronological age is 48. My biological age, based on my most recent blood markers is 35.

That's a 13-year difference — and one I'm actively working to maintain.

Most of us think of age as something that's fixed. Your chronological age is simply the number of years you've been alive, and that number is going to keep ticking upwards.

But biological age is different.

What exactly is biological age?

Biological age gives us another way of looking at how well the body is ageing.

Two people can both be 50, for example, but have very different metabolic health, inflammation, organ function and physiological resilience. Their biological age may reflect some of those differences.

And unlike your chronological age, aspects of biological ageing are dynamic. Our bodies are constantly responding to nutrition, movement, sleep, stress and our environment.

How do you actually measure it?

PhenoAge — how old do you appear to be biologically?

PhenoAge is a biological age calculation based on nine routine blood biomarkers, together with your chronological age. These markers reflect different aspects of physiological health, including inflammation, metabolism and organ function. [6]

This is the calculator I use on my website because it's accessible, uses blood markers that many people are already having tested, and has been extensively studied in large population datasets. [6]

Think of PhenoAge as a snapshot — an estimate of where your biological age sits right now.

It's one useful lens on biological ageing, but it's not the whole picture.

DunedinPACE — how fast are you ageing?

DunedinPACE asks a different question.

Rather than giving you a biological age, it estimates your pace of ageing using patterns of DNA methylation. [1]

Think of it like your speedometer.

A score of 1.0 represents the average rate of ageing — roughly one biological year for every calendar year that passes.

A score below 1.0 means you're ageing more slowly than average. A score above 1.0 means you're ageing faster.

So a score of 0.8 would mean you're ageing at approximately 0.8 biological years for every year that passes.

DunedinPACE is one of the most extensively studied measures of the pace of biological ageing and has been associated with a range of health and ageing outcomes. [1]

What about epigenetic age?

This is where things get even more interesting.

Epigenetic age is measured using patterns of methyl groups attached to DNA at specific sites across the genome.

These patterns change throughout our lives and can be influenced by ageing, nutrition, lifestyle and other environmental factors.

There are now a number of different DNA methylation clocks, each designed to capture different aspects of ageing. [5]

And the field is moving quickly.

Newer approaches are beginning to look beyond a single biological-age number and explore how different systems of the body may be ageing. One example is TruDiagnostic's TruAge SYMPHONYAge, which looks at ageing across multiple organ and physiological systems.

These newer approaches are an exciting area of research as we learn more about the fact that different parts of the body may not all age at the same rate.

Can biological age actually change?

Yes, and this is why we measure it as part of the protocol at Ageless Nutrition as it gives you a good reference point and one you can actively check in on.

Studies have shown that some measures of biological ageing can change in response to diet and lifestyle interventions. [3, 2]

In an Australian pilot study, Dr Denise Furness and colleagues also found significant improvements in several DNA methylation measures following a three-month nutrition, lifestyle and targeted supplementation program. [4]

Importantly, not every biological-age measure changed in the same way. This is a good reminder that different tests are measuring different aspects of ageing.

Is there one best biological age test?

Not really.

PhenoAge gives you a snapshot based on blood biomarkers. DunedinPACE looks at the rate at which you're ageing. DNA methylation clocks provide another layer of information by looking at patterns of methyl groups attached to DNA.

They're measuring different things, so it's less about finding the best test and more about understanding what each one can tell you.

Want to find out yours?

If you're curious about your biological age, you can use my free biological age calculator to get an estimate based on your existing blood markers.

It's a simple place to start — and you might be surprised by what you find.

Your chronological age is fixed. Your biological age doesn't have to be.

As for me, I'll happily take 35 for now. I'm not about to argue with the numbers.

References

1. Belsky, D. W., Caspi, A., Corcoran, D. L., Sugden, K., Poulton, R., Arseneault, L., Baccarelli, A., Chamarti, K., Gao, X., Hannon, E., Harrington, H. L., Houts, R., Kothari, M., Kwon, D., Mill, J., Schwartz, J., Vokonas, P., Williams, B. S., & Moffitt, T. E. (2022). DunedinPACE, a DNA methylation biomarker of the pace of aging. eLife, 11, e73420. https://doi.org/10.7554/eLife.73420

2. Fiorito, G., Caini, S., Palli, D., Bendinelli, B., Saieva, C., Ermini, I., Valentini, V., Assedi, M., Rizzolo, P., Ambrogetti, D., Ottini, L., & Masala, G. (2021). DNA methylation-based biomarkers of aging were slowed down in a two-year diet and physical activity intervention trial: The DAMA study. Aging Cell, 20(10), e13452. https://doi.org/10.1111/acel.13452

3. Fitzgerald, K. N., Hodges, R., Hanes, D., Stack, E., Cheishvili, D., Szyf, M., Henkel, J., Twedt, M. W., Giannopoulou, D., Herdell, J., Logan, S., & Bradley, R. (2021). Potential reversal of epigenetic age using a diet and lifestyle intervention: A pilot randomized clinical trial. Aging, 13(7), 9419–9432. https://doi.org/10.18632/aging.202953

4. Furness, D., & Taylor, P. (2025). Three-month nutritional and lifestyle intervention reduces biological age: A pilot study using DNA methylation clocks. Journal of the Australasian College of Nutritional and Environmental Medicine.

5. Levine, M. E., Lu, A. T., Quach, A., Chen, B. H., Assimes, T. L., Bandinelli, S., Hou, L., Baccarelli, A. A., Stewart, J. D., Li, Y., Whitsel, E. A., Wilson, J. G., Reiner, A. P., Murray, A., & Horvath, S. (2018). An epigenetic biomarker of aging for lifespan and healthspan. Aging, 10(4), 573–591. https://doi.org/10.18632/aging.101414

6. Liu, Z., Kuo, P.-L., Horvath, S., Crimmins, E., Ferrucci, L., & Levine, M. (2018). A new aging measure captures morbidity and mortality risk across diverse subpopulations from NHANES IV: A cohort study. PLOS Medicine, 15(12), e1002718. https://doi.org/10.1371/journal.pmed.1002718

Clinical disclaimer: This information is for general education and is not a substitute for individual medical advice, diagnosis or treatment. It should always be interpreted in the context of your symptoms, health history and other clinical findings with your qualified healthcare practitioner.