What Is Biological Age and Can You Change It?

Biological age sounds like a simple number. The science behind it isn’t. Here’s what the number can tell you, where it falls short, and whether it can really change.

You know your chronological age. That’s the easy one. It’s simply how many years you’ve been alive.

Biological age is an estimate of how your body is aging based on things like blood markers, physical function, fitness, or molecular changes rather than birthdays alone.

The catch is that there isn’t one accepted test for it. Different methods measure different pieces of aging, and they can give the same person different answers.

Some of those measurements can also change over time. That’s encouraging. It still doesn’t mean a younger biological-age result proves your entire body has literally become younger.

A 2025 systematic review of biological-age research found dozens of methods in use and no agreed-upon gold standard.

At a Glance

• Chronological age is fixed. Biological age is an estimate based on selected markers of aging.
• There is no definitive biological-age test that reveals one “true age” for your whole body.
• Different tests can give different answers because they may measure different parts of aging.
• Some aging-related markers can improve, but a younger score does not prove that aging itself has been reversed.

What is biological age?

Imagine two people who are both 60.

One is active, maintains muscle and fitness, and has healthy blood pressure and blood sugar. The other struggles with stairs and is dealing with several chronic health problems.

Same chronological age. Very different picture.

That difference is essentially what researchers are trying to capture with biological age.

Depending on the method, they may look at blood chemistry, physical performance, cardiovascular function, DNA changes, proteins, metabolites, or several measurements at once.

The important word is estimate.

Biological age isn’t a second birthday hiding somewhere inside your cells. It’s a way of modeling certain parts of the aging process and one piece of the broader picture of healthy aging after 50.

Biological age vs. chronological age

Chronological age answers:

How long have you been alive?

Biological age tries to answer:

How are you aging?

Your chronological age moves forward at the same rate no matter what you do. A biological-age estimate depends on what is measured and which model is used.

So someone who is 65 might get an estimate of 58 from one test and 63 from another.

That starts to make more sense once you look at how these tests work.

How do researchers measure biological age?

There isn’t one method. Researchers have developed several approaches, and they aren’t all looking at the same thing.

Blood and clinical biomarkers

Some models combine familiar health measures such as blood sugar, inflammation, kidney function, blood-cell counts, cholesterol, and blood pressure.

One example is Phenotypic Age, a clinical model that combines chronological age with a group of blood-based biomarkers. It was developed to capture differences in health and mortality risk that chronological age alone may miss.

Many of the inputs come from routine medical tests, which makes this type of approach appealing.

But the final age is still the output of a particular model. It isn’t a direct measurement of how old every part of your body is.

Epigenetic clocks

This is where much of the modern biological-age buzz comes from.

DNA methylation is a chemical modification in which methyl groups are added at certain sites on DNA. Patterns of methylation change with age, which allows researchers to build what are known as epigenetic clocks.

Steve Horvath developed one of the best-known early clocks in 2013. Newer clocks were designed for somewhat different jobs.

DNAm PhenoAge, for example, uses DNA methylation patterns to approximate a clinical measure of phenotypic aging linked with health and mortality risk.

GrimAge uses a different DNA methylation approach that incorporates molecular surrogates related to plasma proteins and smoking history and was designed to predict mortality and other aging-related outcomes.

DunedinPACE takes another approach and estimates the pace of aging rather than giving you an age in years.

The names matter less than the takeaway:

Two tests that both claim to measure epigenetic aging may not actually be measuring the same thing.

Physical and functional measures

Aging also shows up in what your body can do.

Researchers study measures such as cardiovascular fitness, strength, walking speed, mobility, lung function, blood pressure, and cognitive performance.

For adults over 50, those can feel a lot more tangible than a DNA methylation score. Your walking speed won’t hand you an official biological age, but it may still tell you something useful about how well you’re functioning.

That is also the idea behind our guide to simple at-home tests that can tell you something about how you’re aging.

Newer molecular approaches

Researchers are also developing aging models based on proteins, metabolites, immune markers, and combinations of large amounts of biological data.

A 2023 study in Nature, for example, used proteins found in blood to build aging estimates for 11 major organ systems.

These newer approaches are promising research tools. They also make the idea of one neat biological-age number look even less neat.

What about telomeres?

Telomeres are protective structures at the ends of chromosomes, and they generally shorten as cells divide. That made them an obvious target for aging research.

They’re part of the story. They’re not the whole plot.

Telomere length varies between people and can also depend on the tissue and measurement method involved. The Max Planck Institute for Biology of Ageing notes that telomere length alone provides limited information about someone’s biological age.

So a telomere test isn’t exactly an expiration-date decoder ring.

Do you actually have one biological age?

Maybe not.

Different parts of your body don’t necessarily age at the same rate.

That Nature organ-aging study mentioned above is a good illustration: researchers found that organ-specific aging estimates could differ substantially within the same person.

Your heart, kidneys, brain, immune system, and muscles don’t have to march through aging in perfect formation.

That doesn’t make biological age useless. It means the idea that your entire body has one perfectly precise age may be too simple.

For now, these organ-age models are also largely research tools rather than routine medical tests.

Why can different biological-age tests give you different answers?

Say one test tells you your biological age is 55 and another says 62.

Before assuming one of them is nonsense, look at what each test measured.

One may analyze DNA methylation. Another may use blood biomarkers. Another might emphasize cardiovascular fitness or physical function. Even two epigenetic clocks may have been designed to predict different outcomes.

Researchers have found this disagreement too. In one study comparing 11 measures of biological aging in the same people, agreement between the methods was generally low.

There simply isn’t one ruler everyone has agreed to use.

How accurate are biological-age tests?

Accurate at what? That’s the real question.

Some biological-age models have been shown to predict or correlate with meaningful outcomes such as mortality, disease risk, or physical function. Some of the earlier epigenetic clocks were also designed to estimate chronological age with impressive accuracy, while newer clocks may instead focus on health risk, mortality, or pace of aging.

That does not mean they have been validated as a measurement of one person’s single “true” biological age.

No current test can give you one universally accepted age for your entire body.

Keep that in mind when a commercial test promises to reveal your “real age.”

Before paying for one, consider what it measures, what the model was designed to predict, whether it has been independently tested, whether repeat results are reasonably consistent, and whether the answer will actually change anything useful.

The Max Planck Institute advises against using commercial biological-age tests as the sole basis for medical or health decisions.

And if a pricey test ultimately tells you to exercise, sleep better, manage your blood pressure, and stop smoking, you may have bought yourself a very expensive reminder.

Can biological age change?

Some biological-aging measures can change.

A later analysis of the randomized CALERIE trial gives us a particularly useful example.

Researchers followed 220 adults without obesity for two years. Participants assigned to calorie restriction showed a small slowing in DunedinPACE, a DNA methylation measure designed to estimate the pace of aging.

But the same intervention did not significantly change the PhenoAge or GrimAge measures examined in the analysis.

Same people. Same intervention. Different aging measures. Different results.

That’s a pretty good snapshot of why biological age is more complicated than one number.

Blood pressure can improve. Fitness can improve. Blood sugar can improve. Some molecular measures can move in a favorable direction too.

That gives researchers good reason to think that aspects of aging biology are modifiable.

It does not automatically translate to “I became six years younger.”

Can you actually reverse biological aging?

This is where the headlines can get ahead of the science.

You’ve probably seen claims that a diet, supplement, or lifestyle program can “reverse biological age” or “turn back your biological clock.”

Some studies have reported younger readings on certain epigenetic-age measures after an intervention. That’s scientifically interesting.

It isn’t the same as showing that your heart, brain, muscles, immune system, disease risk, and remaining lifespan all became younger by the same number of years.

A clock moving backward tells us the clock moved backward. Figuring out what that change means for disease, function, and lifespan is the harder question.

For now, sweeping claims that someone has definitively reversed human aging deserve a healthy dose of skepticism.

What seems to influence biological aging?

Here we meet a pretty familiar cast of characters.

Physical activity and fitness have some of the better evidence. A 2026 systematic review and meta-analysis covering 44 studies and more than 145,000 people found that higher physical activity was generally associated with younger readings on some DNA methylation clocks. Much of the research was observational, so it can’t prove exercise directly caused those differences.

Muscle and strength matter enormously for function as we age, regardless of whether anyone assigns them a biological-age number. Maintaining strength supports mobility, independence, and resilience.

Metabolic and cardiovascular health also show up repeatedly in biological-age research. Blood pressure, glucose regulation, inflammation, and other clinical measures are direct inputs in some biological-age models.

Smoking, diet, alcohol use, and other lifestyle factors have also been linked with biological-aging measures. A 2024 review found that these relationships were generally more consistent for physiological measures than for molecular measures such as epigenetic clocks and telomeres.

Sleep belongs in the conversation too. Short sleep and insomnia have been associated with older readings on some epigenetic-aging measures. That doesn’t prove fixing your sleep will automatically make a biological-age test spit out a younger number.

And this isn’t purely a personal-discipline contest. A 2026 systematic review and meta-analysis of 140 studies found that socioeconomic conditions were associated with epigenetic aging, with stronger relationships seen for some newer generations of aging clocks.

Biology reflects more than what you ate for lunch or whether you made it to the gym.

The useful takeaway isn’t that there’s one perfect anti-aging routine. It’s that many of the habits and health factors that support healthy aging also show up in biological-aging research.

What matters more than your biological-age number?

It would be nice to open an app every birthday and discover you somehow stayed 47.

Your body has more important things to do.

After 50, it’s generally more useful to pay attention to whether you’re maintaining strength and mobility, staying active, protecting cardiovascular and metabolic health, sleeping reasonably well, and remaining able to do the things that matter to you.

Those real-world measures are also among the signs you may be aging well.

A biological-age estimate can add information to that picture. It shouldn’t become the whole picture.

A better way to think about your biological age

Treat biological-age information as a signal, not a verdict.

If a useful measurement points to something worth paying attention to, great. If a relevant marker improves over time, that’s encouraging too.

But chasing the youngest possible number misses the point.

The goal is better health, function, and resilience, not winning an argument with your birth certificate.

Curious about how your habits line up with healthy aging?

Take the WHN Aging Profile Score to get a closer look at habits and health markers that may be worth paying attention to.

The WHN Aging Profile Score is not a clinical biological-age test and does not claim to determine the literal age of your body.

Bottom Line

Biological age is a legitimate scientific concept, but it isn’t one magic number.

Researchers can measure different parts of aging, and some of those measures can change. Different tests can also give different answers because they aren’t necessarily looking at the same thing.

The useful goal isn’t proving you’re five years younger than your driver’s license. It’s improving the health and function those measurements are trying to capture.

FAQ

Can your biological age be younger than your chronological age?

Yes. Some models can produce a biological-age estimate below your chronological age. That generally means the markers used by that particular model look more like patterns seen in younger people. It does not mean every organ or system in your body is literally that age.

How do you determine your biological age?

There isn’t one method. Researchers use combinations of blood and clinical biomarkers, DNA methylation clocks, physical and physiological measurements, and newer molecular approaches. Different methods can produce different results.

Are biological-age tests accurate?

Some biological-age models can predict or correlate with specific age-related outcomes or track particular molecular patterns. There is currently no universally accepted test that determines one definitive biological age for an individual.

Can you lower your biological age?

Some biological-age estimates and aging-related biomarkers can move in a favorable direction. Whether that counts as “lowering your biological age” depends on what is being measured. It should not automatically be interpreted as whole-body age reversal.

Is biological age the same as metabolic age?

No. Metabolic age is usually a consumer estimate based on metabolism and body composition, often comparing estimated basal metabolic rate with population averages. Biological age is a broader scientific concept that can incorporate molecular, clinical, physiological, and functional measures.