From the blog
Biological Age Tests: How They Work and How Accurate They Are
In short: A biological age test estimates how your body is ageing, compared with your age in years. The main types read chemical tags on DNA, combine routine blood results, or measure telomeres, the protective ends of chromosomes. These tests can show risk patterns across large groups of people. A biological-age score alone cannot diagnose or rule out illness; individual blood tests may contribute to diagnosis. A single number for one person also carries real uncertainty. Different tests can also give different answers.
What is biological age?
Biological age is an estimate of how far your body has aged, based on measurements taken from it. Chronological age is simply the number of years since you were born.
Two people aged 50 can differ widely in health. Biological age tries to put that difference into a single figure. It is an estimate from a formula, not a fixed fact about you.
How is biological age calculated?
Biological age is calculated by feeding measurements from your body into a formula built from large studies of people. Researchers first find which measurements track with age, illness or death. They then build a formula, often called a clock, using those findings. Your own results go in, and an age comes out.
So the answer depends on the formula. Different clocks were built on different data, to predict different things.
What are epigenetic clocks?
Epigenetic clocks are formulas that estimate age from DNA methylation, the pattern of small chemical tags on your DNA. These tags help control which genes are switched on. They do not change the DNA code itself, but the pattern shifts as you age.
There are two main kinds of clock:
Clocks trained on age. The Horvath clock, published in 2013, uses 353 sites on DNA to estimate age across most tissues and cell types.
Clocks trained on health. DNAm PhenoAge, published in 2018, was built using clinical measures of ageing, and it predicted death from any cause and healthspan better than earlier measures in that study.
What is PhenoAge and can a blood test estimate biological age?
Yes. PhenoAge, also called Phenotypic Age, estimates biological age from your age in years and nine routine blood results. Those results are albumin, creatinine, glucose, C-reactive protein (a marker of inflammation), lymphocyte percentage, mean cell volume, red cell distribution width, alkaline phosphatase and white blood cell count.
In a study of more than 11,000 US adults, followed for up to 12.6 years, an older Phenotypic Age was linked with a higher risk of death, even after allowing for age in years. The authors said more evaluation in other groups is needed.
Do not confuse this with DNAm PhenoAge. That one is a DNA methylation test, which needs a different laboratory method.
Routine blood results can shift for short-term reasons. A passing infection can raise C-reactive protein and white cells, for example, and the score may move with them. This is why a doctor should read the result alongside your health at the time of the test.
What does a telomere test show?
A telomere test measures the protective caps at the ends of your chromosomes, and it gives a rough signal of cell ageing rather than an age you can rely on. Telomeres shorten with cell division and oxidative stress. Studies usually measure them in white blood cells.
A review in Epidemiologic Reviews found that shorter telomeres were linked with older age and male sex, while links with other health markers were uncertain. Studies conflicted, which fuelled debate on telomere length as a measure of overall ageing.
Measurement is also a problem. A 2021 review of 25 studies comparing common laboratory methods found wide variation in how well methods agreed, and poor reporting of how the tests were done. Sample sizes ranged from 12 to 181; only seven studies included more than 100 samples.
Do different biological age tests agree?
Often they do not. In a study of 964 middle-aged people in New Zealand, researchers compared 11 measures, including telomeres, epigenetic clocks and blood-marker scores, in the same people. Agreement between the measures was low. Their links to physical function and other signs of ageing were modest, and the authors said the measures may not capture the same aspects of ageing.
You may therefore get a "younger" result on one test and an "older" result on another. Neither one is automatically wrong. They may be measuring different things.
How accurate and repeatable are biological age tests?
Repeatability varies by test, and it can be poorer than people expect. In a 2022 study, technical noise alone produced differences of up to 9 years between repeat measurements of the same sample, across six well-known epigenetic clocks. Retrained versions of those clocks brought most repeats within 1.5 years.
This matters for anyone tracking change. A drop of one or two years on a repeat test may be real, or it may be noise. To make a fair comparison, ask which clock is used, and ask whether it has been tested for repeatability. Use the same test, the same laboratory and the same type of sample each time.
A 2026 review said that race, sex and age all affect how well these measures predict health, and that using them in everyday practice has been challenging. Much of the research above comes from outside India, so ask whether a test has been checked in Indian adults.
What can a biological age test tell you, and what can it not?
A biological age test can give you a talking point and a baseline, but it cannot tell you what will happen to you. Here is a simple summary.
It can:
give an estimate that researchers link with health risk across large groups
add a further view to your standard blood tests
help assess change over time when the method is sufficiently repeatable and measurement variation is considered
It cannot:
diagnose or rule out illness from the score alone, although individual blood tests may contribute to diagnosis
tell you how long you will live
replace the screening tests your doctor advises
show on its own that a treatment or supplement has worked
tell you which organ or habit is responsible for the result
A "young" result does not mean you can skip your regular check-ups. An "old" result is not a diagnosis, and it should prompt a calm talk with your doctor.
Is a home biological age test reliable?
A home kit can be convenient, but its reliability depends on the laboratory, the clock and the sample. Kits usually use a finger-prick of blood, saliva or a cheek swab, which you post to a laboratory. Lifestyle questionnaires estimate from your answers. Some online calculators instead apply published formulas to laboratory results; their usefulness depends on the measurements and formula.
Before you buy a test or send a sample, ask:
Which clock or formula does it use, and is it published?
Was it checked on this type of sample, such as blood or saliva?
How close are repeat results on the same sample?
Has it been studied in Indian adults?
Who will read the result with me?
What happens to my DNA data, and can it be deleted?
Cost depends on the test and on what your doctor advises.
How does a SOMA doctor decide what is right for you?
SOMA uses biological age indicators as one part of a wider assessment, not as a stand-alone result. Its first assessment includes blood work, hormone panels, and metabolic and inflammatory markers, along with these indicators. Together they set a baseline and show what to track.
A SOMA doctor reviews the results with you and suggests only the tests that make sense for you. Follow-up testing is used to review your longevity plan, as one part of a plan built around you. These assessments are not a substitute for conventional diagnosis, and results vary from person to person.
SOMA centres in Mumbai and New Delhi
SOMA doctors see patients at two centres:
Mumbai: A-507, Kohinoor Square, N.C. Kelkar Marg, Shivaji Park, Dadar West, Mumbai 400028. Phone +91 98671 94033.
New Delhi: E-354, Greater Kailash II, New Delhi 110048, serving Delhi NCR and Gurugram. Phone +91 87969 92001. More about the New Delhi centre.
The New Delhi centre is independently operated under licence from SOMA Longevity Sciences, and its own doctors lead care there. Both centres follow the same SOMA assessment and diagnostic standards. Online consultations are also available. Contact either centre.
Questions people ask
What is the difference between biological age and chronological age?
Chronological age is the number of years since you were born. Biological age is an estimate of how far your body has aged, calculated from measurements such as DNA tags or blood results. The two can differ, and different tests can give different biological ages.
Is there a blood test for biological age?
Yes. PhenoAge uses your age and nine routine blood results. Epigenetic clocks also often use a blood sample, but they read DNA methylation, which is a different laboratory method. A biological-age score alone cannot diagnose or rule out illness; individual blood tests may contribute to diagnosis.
How accurate is a biological age test?
Accuracy varies by test, and no single test is a gold standard. In one study, technical noise alone moved six well-known epigenetic clocks by up to 9 years between repeat measurements. Improved versions brought most repeats within 1.5 years. Different types of test can also disagree.
Can I do a biological age test at home?
Some kits let you collect blood, saliva or a cheek swab at home and post it to a laboratory. Ask which clock is used, whether it was checked on that sample type, and how repeatable it is. Questionnaires only give a rough estimate.
Where can I get a biological age test in Mumbai or Delhi?
Ask a doctor first, who can explain which test suits you and how to read it. SOMA uses biological age indicators in its assessment at its centres in Dadar West, Mumbai and Greater Kailash II, New Delhi, alongside standard blood and hormone panels.
Related guides
Sources
Horvath S. DNA methylation age of human tissues and cell types. Genome Biology 2013;14(10):R115. https://pubmed.ncbi.nlm.nih.gov/24138928/
Levine ME et al. An epigenetic biomarker of aging for lifespan and healthspan. Aging 2018;10(4):573–591. https://pubmed.ncbi.nlm.nih.gov/29676998/
Liu Z et al. A new aging measure captures morbidity and mortality risk across diverse subpopulations from NHANES IV: a cohort study. PLoS Medicine 2018;15(12):e1002718. https://pubmed.ncbi.nlm.nih.gov/30596641/
Belsky DW et al. Eleven telomere, epigenetic clock, and biomarker-composite quantifications of biological aging: do they measure the same thing? American Journal of Epidemiology 2018;187(6):1220–1230. https://pubmed.ncbi.nlm.nih.gov/29149257/
Higgins-Chen AT et al. A computational solution for bolstering reliability of epigenetic clocks: implications for clinical trials and longitudinal tracking. Nature Aging 2022;2(7):644–661. https://pubmed.ncbi.nlm.nih.gov/36277076/
Sanders JL, Newman AB. Telomere length in epidemiology: a biomarker of aging, age-related disease, both, or neither? Epidemiologic Reviews 2013;35(1):112–131. https://pubmed.ncbi.nlm.nih.gov/23302541/
Lindrose AR et al. Method comparison studies of telomere length measurement using qPCR approaches: a critical appraisal of the literature. PLoS One 2021;16(1):e0245582. https://pubmed.ncbi.nlm.nih.gov/33471860/
Tuminello S et al. Integrating biological aging into clinical practice: a review and path forward for precision longevity medicine. GeroScience 2026, online ahead of print. https://pubmed.ncbi.nlm.nih.gov/42631826/
This article is for education and general information. It is not a substitute for a medical consultation, diagnosis or treatment. Results vary by individual biology.
Wondering what your own results would show? Start with a conversation.