Biological Age vs Chronological Age: What Science Says

You know exactly how old you are. It’s on your licence, your passport, and your birthday cake.

But that number tells you only one thing: how much time has passed since you were born. It doesn’t tell you how your body is ageing. That distinction sits at the centre of a fast-moving area of longevity science: biological age.

Same Age, Different Bodies

Picture two people, both 45. They’ve lived the same number of years. Their cardiovascular health, metabolic function, strength, recovery, inflammation and disease risk can still look nothing alike.

This is why researchers separate chronological age from biological age. Chronological age is simply time passed. Biological age estimates the physiological changes accumulating inside the body.

The US National Institute on Aging frames it plainly: some people stay healthy and disease-free well into later life, while others develop age-related conditions much earlier, even at the same chronological age. Same number on paper. Different story underneath.

What Shapes Biological Age?

Many factors influence biological ageing, and researchers are still working to understand how they interact. Genetics play a role, but they are only part of the picture. Sleep, physical activity, diet, smoking, alcohol use, stress and environmental exposures have all been studied in relation to ageing and age-related health.

These factors can affect processes such as inflammation, cardiovascular health, metabolism, muscle function and cellular repair. Over time, these changes can contribute to differences in how people age, even when they have the same chronological age.

This doesn’t mean that one habit determines your biological age. Ageing is complex. Biological age reflects the combined effects of many processes happening across the body.

How Scientists Measure Biological Age

Scientists are building biological-age measures from different types of data, including clinical biomarkers, physical function and molecular signals such as proteins, metabolites and DNA methylation.

One well-studied approach looks at DNA methylation, chemical changes to DNA that shift as we age. Scientists use these changes to create what are known as epigenetic clocks. Early clocks were mainly built to estimate a person’s chronological age. Newer versions look beyond age to explore health, mortality risk and how quickly a person is ageing biologically.

One example is DunedinPACE, a measure to estimate how quickly the body is ageing. It was developed using more than 20 years of health data from the Dunedin Study, combined with DNA methylation data from blood. In a 2022 study, faster biological ageing measured by DunedinPACE was linked with poorer physical and cognitive function and more health problems.

Looking Beyond How You Feel Today

This was never really about age. It was about how your health is changing over time.

Most people know their weight, and perhaps their blood pressure or cholesterol. More people now track sleep, heart rate, steps and recovery. But few take a step back and look at what these numbers might tell them about where their health is heading.

That’s where biological age becomes interesting. Not as a score to obsess over. Not a competition to get “younger.” But it’s another lens for understanding your health.

For someone focused on performance, it raises an important question: is the lifestyle that supports performance also supporting long-term health? For those who already exercise and eat well, it offers a chance to look beyond those habits and understand what is actually changing inside the body.

And for anyone thinking about their long-term health, it shifts the question from “Am I sick?” to “What can I learn now that could help me make better decisions later?”

The Number Is Only the Starting Point

A biological age estimate isn’t an outcome on its own. A report can’t make you healthier, a single number can’t tell the full story of your body, and a lower biological age result doesn’t mean ageing has been reversed.

The number is only part of the picture. What matters is understanding what the data is showing, identifying where there is room to act, taking an informed step, and measuring again to see what has changed.

A More Connected Approach to Longevity

This is the idea behind SOMA Longevity. We don’t think the future of health is about collecting more data. It’s about connecting that data, helping you understand what it means for you, turning it into a personalised next step, and continuing to measure how your body responds.

SOMA Longevity is coming soon, with biological and cellular insight designed to sit alongside broader health data, clinical guidance, movement and recovery.

Understand. Act. Measure. Improve. Training for Longevity was never about chasing a younger number. It’s about using what we can learn today to protect how you want to feel, perform and live tomorrow.

SOMA Longevity is coming soon. Membership will be strictly limited. Be among the first to experience SOMA Longevity, with priority access when Founding Membership applications open.

You can book a tour of the SOMA facility to meet the team, explore the space, and learn more about our approach to longevity.

Frequently Asked Questions

Can biological age be reversed, or can it only be slowed?

Some studies have found that biological-age scores can decrease after lifestyle changes. A 2021 randomised trial by Fitzgerald and colleagues found that an 8-week diet and lifestyle programme was linked to a reduction in DNA-methylation age.

A later correction reported an average reduction of 2.04 years in the intervention group. However, it was a small study, and larger, longer studies are needed. A lower epigenetic-age score does not necessarily mean ageing itself has been reversed.

How often should you measure your biological age?

There is no established recommendation for how often to measure biological age. A first test can provide a baseline, while repeating the test later can help show whether your result has changed over time.

The timing depends on the test being used, as different biological-age measures have different levels of stability. Testing too often can make small changes difficult to interpret, as they could reflect normal variation rather than a meaningful change.

Is biological age the same across different organs and tissues?

No. Different parts of the body can age at different rates. A 2023 Nature study led by researchers including Tony Wyss-Coray used blood proteins to estimate the age of 11 major organs in 5,676 adults. Nearly 20% showed accelerated ageing in at least one organ, while only 1.7% showed it across multiple organs. This suggests that a whole-body measure does not always show what is happening in individual organs.

Does biological-age testing work the same way for men and women?

Biological ageing and DNA-methylation patterns can differ between males and females, which can affect some biological-age measures. Hormonal changes, including those linked to menopause, are also being studied.