Biological age tests: what they measure, and what an organ age score means

Quick answer: Your chronological age is how many birthdays you’ve had. A biological age test estimates how old your body seems, based on things like the chemical marks on your DNA, proteins in your blood, or your fitness. People use it to see how they’re aging and to check whether the changes they make are working. Since nobody can wait decades to see who lives to 100, biological age gives you a number you can track now.

Your age vs your biological age

Chronological age is the date on your birth certificate. But two people born the same year can be in very different shape. One runs marathons at 60, another struggles with stairs at 50.

Biological age puts a number on that difference. Researchers study large groups of people, learn which patterns show up in the body at each age, and compare your results to those patterns. If your body looks more like a typical 44-year-old’s than a 50-year-old’s, your biological age may come back as 44.

The same gap shows up between whole countries. A 2025 study used health data from around the world to estimate biological age country by country, based on how many age-related health problems people had. Among 65-year-old men, the average biological age ranged from 61 to 74 depending on where they lived. That’s a 13-year spread for people with the same birthday.

And it can move. Between 1990 and 2019, 65-year-olds in most wealthy countries became biologically younger, by up to about two and a half years. Biological age isn’t fixed. Whole countries have shifted it, and so can one person.

Why biological age matters so much in longevity

That number turns out to be very useful, and here’s why. The real goal of longevity care is for people to live longer and stay healthy for more of those years. But if you wanted to know whether something actually helps people live to 90 or 100, you’d have to wait decades to find out.

That’s far too slow, both for research and for you as a person deciding what to do this year. So researchers look for measurements that change sooner and show how fast aging is happening. Biological age is one of the main ones.

Think of training for a marathon. You don’t wait until race day to find out whether your training is working. You check your pace on shorter runs along the way. Biological age tests are those shorter runs for aging.

Breaking aging into smaller pieces helps too. Instead of one number for the whole body, newer tests look organ by organ, because your heart, brain and kidneys don’t always age at the same speed. A large 2023 study in Nature used blood proteins from 5,676 people to estimate the age of 11 organs, and found that many people had one organ aging much faster than the rest.

Those links come from large groups of people followed over time. A single test can’t predict what will happen to you, but they show why measuring aging organ by organ has caught on so quickly.

What makes a body, or an organ, age faster?

Biological age isn’t fixed by your birthday or your genes alone. Everyday habits show up in these tests too. Here are some of the clearest examples from research.

Health problems also tend to snowball. Across many countries, the number of age-related health problems people have grows by about 3% a year, and each new problem makes the next one a little more likely. That’s why changes made earlier tend to pay off more.

These links come from studies of large groups, so they show patterns, not guarantees. But the encouraging part is that most of these are things you can change, which is exactly why people retest to see if their changes are working.

How to get your biological age tested

There are two main ways, and both are simple.

Most tests look at one of three things. Epigenetic tests read chemical marks on your DNA that change as you age. Organ age tests look at proteins in your blood. And some clinics combine ordinary lab results, like blood sugar, inflammation and kidney markers, into one age-like score. Your fitness, such as your VO2 max and grip strength, doesn’t come out as an “age,” but it tracks closely with how well people age, and many clinics measure it alongside.

Whichever route you choose, stick with the same test from the same company each time, so your next result can be compared fairly with your first.

How clinics and online memberships do it

Different places use different tests, so it helps to know what you’re actually getting. Here are a few real examples.

Online memberships. Function Health and Superpower are national memberships that run a large blood panel at a partner lab and show you a biological age alongside your results. Both calculate it from your regular blood markers, things like blood sugar, inflammation and kidney function, rather than from your DNA. Superpower says its number is a PhenoAge estimate, a well-known research formula built from routine blood tests. Function describes its score as different from DNA-based tests. The upside is that it comes with blood work you’re already getting. The trade-off is that it’s a different kind of number from an epigenetic test, so the two can’t be compared directly.

Clinics that use a DNA test. Many clinics we list send a blood sample for an epigenetic test, which reads the chemical marks on your DNA. Next Health includes a TruAge epigenetic test in its Executive Physical. Longevity Medical Clinic in Kirkland uses myDNAge, another DNA methylation test. Fountain Life in White Plains includes an epigenetic age reading in its assessment.

Clinics that use more than one measure. Some clinics combine several tests, because each one sees a different part of the picture. Cenegenics San Francisco lists two biological age measures, one of them PhenoAge. BluePath Longevity in Chicago runs an epigenetic aging test and a separate brain aging analysis, and the Northwestern Medicine Human Longevity Clinic uses several different measures of biological age.

Across the clinics we track, more than 30 publish a biological age test. When you compare them, ask which test they use, whether it’s from blood or saliva, and whether a doctor goes through the result with you.

Age vs pace of aging

Some tests tell you an age. Others tell you a pace. It’s worth knowing which one you’re getting.

Think of a car. The odometer shows how many miles it has done in total. The speedometer shows how fast it’s going right now. An age score is like the odometer: how much aging seems to have built up. A pace score is like the speedometer: how fast it seems to be happening at the moment. Both can be useful, but they answer different questions, so ask the clinic which one their test reports.

What is an organ age test?

Organ age tests are a newer idea. Instead of one number for your whole body, they try to estimate whether specific organs, like your heart, brain, kidneys or liver, look older or younger than expected.

They grew out of research like the 2023 Nature study above. Commercial organ age tests are inspired by that work, though each company uses its own set of proteins and its own model.

One thing to keep in mind: an organ age score comes from a blood test, not from looking at the organ itself. A “heart age” from blood proteins is more like a smoke alarm in one room than an inspection of the wiring. It might suggest a room worth checking. The actual check is a test that looks at that organ directly, such as a heart scan or an ultrasound, which your doctor can help you decide on.

How accurate are biological age tests?

This is the most common question, and it deserves a straight answer. Biological age tests are useful, but they’re less precise than the number on your report makes them look. Knowing why helps you use them well.

They aren’t standardized yet. No consumer biological age test is FDA-approved to diagnose anything. They’re sold as wellness tests, and most insurance doesn’t cover them. There’s also no shared reference standard, so each company uses its own lab methods and its own formula, and many don’t say which formula they use.

Every reading has a margin of error. Researchers estimate that many DNA-based tests are off by about three years either way. So a result that says you’re three years older than your age could, in reality, mean you’re right on track, or even a little younger. The first well-known DNA clocks were off by about 2.9 and 3.9 years on average, and some older versions gave readings up to nine years apart when the same blood sample was tested twice. Newer versions have cut that to under a year.

Different tests measure different things. A DNA test, a blood-marker score like PhenoAge, and an organ protein test are each looking at a different part of aging. So it’s normal for two of them to give you two different ages. The sample matters too: in one 2025 study, some DNA clocks read up to 30 years older from saliva or cheek swabs than from blood, because they were built on blood.

That might sound discouraging, but it shouldn’t put you off. Think of a bathroom scale that’s off by a couple of pounds. It’s not great for your exact weight, but if you use the same scale every week, it’s very good at showing whether you’re going up or down. Biological age tests work the same way: they’re most useful for following your own trend on the same test, not for a one-time verdict.

And the science behind them is real. In large studies, people whose blood-based biological age was higher had a higher risk of dying over the following years, about 9% higher for each extra year. That’s why researchers keep using these tests, and why a clinic will read your result next to your other numbers rather than on its own. Our guide to measured vs derived biomarkers explains why a number that comes out of a formula behaves differently from one a lab measures directly.

What your result can mean, and what a clinic does with it

You shouldn’t have to interpret a biological age score on your own. A good clinic reads it alongside your other results, explains what it means, and turns it into a plan. Here are a few common situations. They’re illustrations, not advice; your own doctor will look at your full picture.

A score on its own is a conversation starter. What you do about it comes from the numbers around it. If your biological age improves and your blood sugar, cholesterol and fitness improve too, that’s a picture you can trust much more. For how clinics build that plan and decide what to retest, see baseline testing vs retesting.

What a biological age test costs

Some clinics include one in a wider assessment or membership. These tests are almost always self-pay. For a wider look at prices, see how much longevity clinics cost.