Contents
What kind of number did you get?
Start with the label on your result. The kind of number changes what it means.
Most common
An age in years
Often shown as a gap from your calendar age. A biological age of 47 for someone who is 50 is a gap of three years below calendar age. Researchers call a gap above calendar age “age acceleration”. Despite the name, it describes a difference at one moment, not a speed.
Some tests
A pace of aging
Some tests also give a pace, where 1.0 is the average of the group the clock was built on. A pace result is an estimate, not an exact personal speed.
Extras
Other scores
Not every number called a “rate” is a pace: some are simply your biological age divided by your calendar age. Reports may add ages for organs or body systems, or a percentile that ranks you against a comparison group the company chose. What these extra scores rest on differs from test to test.
An age from a clock trained on health and survival data, such as PhenoAge or GrimAge, is a risk score turned into an age. It is not a count of years of life left. See three kinds of result for the difference between age-like, risk-like and pace results.
Older or younger than your age: what does it mean?
In large population studies, clocks trained on health measures, such as GrimAge, PhenoAge and DunedinPACE, are linked to the risk of death and disease even after taking calendar age into account. On average, people whose results on these clocks were older than expected for their age, or faster in pace, had a higher risk. Clocks built only to predict age show weaker, less consistent links.
These are findings about groups, not a forecast for you.
How precise is one result?
In research studies, two kinds of repeat measurement gave very different pictures:
The same blood sample, measured twice
Most DNA methylation clocks gave closely matching results when this was done in the same lab.
Separate samples, hours or days apart
Blood samples from the same person varied much more.
So a single result is less exact than one number suggests.
A result can also reflect a temporary state. In one research study with small groups of people, some clock readings were higher after emergency surgery, during severe COVID-19 and around childbirth, and came down again, fully or partly, in the days or weeks that followed. Whether such short-lived changes matter for health is not known. Blood is also a mix of immune cells, and that mix can move DNA methylation results.
Comparing with an earlier result
Before you read meaning into a change, check these points.
Before you compare two results
- Results are easiest to compare when they come from the same test. A different test reads different things and was built to predict different things, so a different number does not by itself mean you changed.
- Even the same test can change: labs and companies sometimes update their methods or formulas between your tests.
- None of the sources we reviewed says how big a change in one person’s result is meaningful for a consumer test. A small change between two tests may be noise.
- If a company quotes how repeatable its test is, check whether that figure comes from measuring the same sample twice. In research on DNA methylation clocks, separate blood samples taken hours or days apart varied more than one sample measured twice.
- A score that goes down is not yet proof of better health: it has not yet been shown that changing a clock score makes people live longer or healthier lives.
There is no agreed interval for retesting. For what to weigh when you decide, see how often to test.
Thinking about another test?
Compare shows what each test measures and reports, and the quiz suggests a type of test to start with.
It is not a diagnosis.
A biological age result shouldn’t be used on its own to make medical decisions. Experts in the field say it still has to be shown, in clinical trials, that using these results in medical care improves people’s health.
It doesn’t say why.
On its own, a biological age number doesn’t tell you why it is what it is, or which part of your body is behind it. Some reports add scores for organs or body systems; these are statistical estimates too, not a medical check of those organs or systems.
More on this in the limitations of aging clocks.
When to talk to a doctor
This is general information, not medical advice. Three situations where a doctor is the right next step:
- Flagged blood valuesSome tests work out a biological age from routine blood tests. One published method, Phenotypic Age (the blood-test version of PhenoAge), uses values such as blood sugar, albumin, creatinine and C-reactive protein. Each of these values also has its own medical meaning. If your report shows them and any are flagged as outside the laboratory’s reference range (the range typical of healthy people), it’s worth discussing with a doctor, whatever your biological age. A flag is not a diagnosis: some healthy people’s results fall outside the range too.
- Symptoms or worriesA result younger than your calendar age does not rule out illness: biological age tests have not been validated as a way to check for disease. If you have symptoms or health worries, talk to a doctor, whatever your score.
- Before changing treatmentTalk to a doctor before you start, stop or change any medicine, supplement or other treatment because of a biological age result.
Show all 20 sources, with our notes on authors' ties to test makers where relevant
- Moqri et al. (2024). Validation of biomarkers of aging. Nature Medicine. Many authors declare ties to clock developers or test companies.
- Moqri et al. (2023). Biomarkers of aging for the identification and evaluation of longevity interventions. Cell. Consensus review by the Biomarkers of Aging Consortium, whose members include clock developers.
- Horvath (2013). DNA methylation age of human tissues and cell types. Genome Biology. The author is a named inventor on a university patent application.
- Levine et al. (2018). An epigenetic biomarker of aging for lifespan and healthspan. Aging. Two authors are named inventors on a university patent application.
- Liu et al. (2018). A new aging measure captures morbidity and mortality risk across diverse subpopulations from NHANES IV. PLoS Medicine. Written by the Phenotypic Age developers.
- Lu et al. (2019). DNA methylation GrimAge strongly predicts lifespan and healthspan. Aging. Written by the clock’s developers; two are named inventors on a university patent application.
- Belsky et al. (2022). DunedinPACE, a DNA methylation biomarker of the pace of aging. eLife. Several authors are inventors of DunedinPACE, which is licensed to TruDiagnostic.
- Balachandran et al. (2025). Pace of Aging analysis of healthspan and lifespan in older adults in the US and UK. Nature Aging. The senior author and two co-authors are DunedinPACE inventors; another co-author founded Oken Health.
- Faul et al. (2023). Epigenetic-based age acceleration in a representative sample of older Americans. PNAS. No competing interests declared; one author developed PhenoAge.
- Sehgal et al. (2026). Biological versus technical reliability of epigenetic clocks and implications for disease prognosis and intervention response. Aging Cell. Two authors are co-inventors of another clock and have consulted for test companies.
- Higgins-Chen et al. (2022). A computational solution for bolstering reliability of epigenetic clocks. Nature Aging. Two authors built clock metrics licensed to a test company.
- Poganik et al. (2023). Biological age is increased by stress and restored upon recovery. Cell Metabolism. Small groups of people. No competing interests declared, though co-authors include GrimAge’s developers, and the study’s new methylation data was generated through the Epigenetic Clock Development Foundation, which one of them founded.
- Sehgal et al. (2025). Systems Age: a single blood methylation test to quantify aging heterogeneity across 11 physiological systems. Nature Aging. Four authors are named inventors on a patent application for the method; two have consulted for test companies.
- Tomusiak et al. (2024). Development of an epigenetic clock resistant to changes in immune cell composition. Communications Biology. Two authors are co-inventors on pending patents.
- Waziry et al. (2023). Effect of long-term caloric restriction on DNA methylation measures of biological aging in healthy adults from the CALERIE trial. Nature Aging. Two authors are DunedinPACE inventors.
- Cummings and Kritchevsky (2022). Endpoints for geroscience clinical trials: health outcomes, biomarkers, and biologic age. GeroScience. One author has consulted for a biotechnology company.
- Ozarda (2016). Reference intervals: current status, recent developments and future considerations. Biochemia Medica.
- Jones and Barker (2008). Reference intervals. Clinical Biochemist Reviews.
- Orth (2021). Direct to consumer laboratory testing (DTCT): opportunities and concerns. EJIFCC.
- US Food and Drug Administration. Direct-to-consumer tests.
This article was prepared with AI assistance from research ledgers that a separate AI reviewer checked against the sources. No external expert validation. Sources checked 21 October 2026. See our methodology or report a correction.