Your biological age is how old your body actually behaves, which can be quite different from the number of birthdays you’ve counted. Two people can both be 50 on paper, yet one has the cardiovascular system, cell function, and disease risk of a typical 42-year-old while the other looks more like 60 under the hood. That gap is what biological age tries to capture. Over the last decade, scientists have built tools — called epigenetic clocks — that estimate it from a blood or saliva sample. This guide explains what biological age means, how it’s measured, and what the evidence says you can actually do to lower it.
Quick answer
- Chronological age = time since you were born. Fixed, unchangeable
- Biological age = how aged your cells and systems are. Variable, partly within your control
- Epigenetic clocks estimate biological age from DNA methylation patterns
- The main ones: Horvath (first-generation), plus newer tools like GrimAge and DunedinPACE, which measures your pace of aging
- What lowers it (best evidence): exercise, not smoking, good sleep, a plant-forward diet, healthy weight, strong social ties
- What doesn’t (reliably): most “anti-aging” supplements and biohacks
Biological vs chronological age
Chronological age is just the calendar — you can’t change it. Biological age is the interesting one because it reflects the wear and repair happening in your body, and that’s influenced by how you live.
When your biological age is lower than your chronological age, it generally signals lower risk of age-related disease and death. When it’s higher — what researchers call age acceleration — it tracks with worse outcomes. The whole appeal of measuring biological age is that, unlike your birthday, it can move.
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The leading way to estimate biological age is through DNA methylation — chemical tags that sit on your DNA and change in predictable ways as you age. By reading methylation at hundreds of specific sites, an algorithm can estimate how old your cells “look.”
The first widely used version came from Steve Horvath in 2013. His multi-tissue clock read methylation at 353 sites and predicted age across most human tissues remarkably well, and it introduced the idea of “age acceleration” — the gap between your methylation age and your real age.1 That paper kicked off the whole field.
| Clock | What it estimates | Generation |
|---|---|---|
| Horvath | DNA methylation age across tissues | First |
| PhenoAge | Aging tied to clinical health markers | Second |
| GrimAge | Mortality and disease risk | Second |
| DunedinPACE | Your current rate of aging | Newer |
DunedinPACE: a speedometer, not an odometer
Most clocks give you an age estimate — an odometer reading. DunedinPACE does something different: it estimates how fast you’re currently aging, like a speedometer. A score of 1.0 means you’re aging about one biological year per calendar year; higher means faster, lower means slower.
It was built from the Dunedin study, a New Zealand birth cohort tracked across two decades on 19 measures of organ-system health. The resulting blood test showed good reliability and was associated with later illness, disability, and death — which is what makes it useful for testing whether an intervention actually slows aging.2 Because it captures your current pace rather than accumulated age, it can pick up changes from lifestyle or treatment faster than odometer-style clocks.
Can you actually lower your biological age?
This is where you need a clear, honest read. The encouraging news: in a randomized controlled trial, two years of mild calorie restriction (about 25% fewer calories) modestly slowed the pace of aging as measured by DunedinPACE — the first evidence from a controlled human trial that a lifestyle change can move a biological-aging marker.3 The effect was small, but even small shifts in aging rate can add up across a population.
The sober news: effect sizes are modest, the clocks are still being refined, and no intervention “reverses” aging in any dramatic, proven way. Be especially wary of products promising to turn your clock back years — the marketing is far ahead of the science.
What the broader evidence supports for keeping your biological age low overlaps almost perfectly with general longevity advice:
- Regular exercise — both aerobic and strength
- Not smoking — smoking is a powerful aging accelerator
- A plant-forward diet with limited ultra-processed food
- A healthy body weight
- Good sleep
- Managing chronic stress — major life stressors have been linked to accelerated biological aging4
- Strong social connections
In other words, the things that lower your biological age are the same longevity habits that predict a longer life overall. See what predicts longevity for the full ranking.
Suggested read: What Is NAD? Plain-English Guide to the Molecule
How exercise and diet fit in
Two levers are worth calling out because they have the most practical support.
Exercise. Regular activity influences many of the systems these clocks measure. Building an aerobic base with zone 2 cardio plus strength work covers the bases; the wider case is in the health benefits of exercise.
Diet. A plant-forward pattern — the Mediterranean diet and Blue Zones diet are the templates — supports healthier aging, and the calorie-moderation seen in that CALERIE trial overlaps with the eating habits of long-lived populations. The research on intermittent fasting sits in the same neighborhood.
Why “reverse aging” claims are mostly hype
The biological-age field has attracted a lot of money and a lot of marketing, and it’s worth understanding why the bold claims outrun the science. The clocks measure correlations — patterns that track with age and risk — not necessarily the underlying causes of aging. Moving a clock reading isn’t the same as proving you’ve made someone healthier or extended their life. That link has to be demonstrated separately, with long follow-up, and for most interventions it hasn’t been yet.
There’s also the problem of different clocks disagreeing. The same blood sample can produce different age estimates depending on which algorithm you run, and an intervention that nudges one clock may leave another unmoved. In the CALERIE trial, calorie restriction shifted DunedinPACE but didn’t significantly move the PhenoAge or GrimAge estimates.3 That’s not a failure — it tells you these tools measure related but distinct things — but it’s a reason to be cautious about any product claiming a clean, dramatic “reversal.”
The honest framing: biological-age measures are promising research tools that are slowly maturing. They are not yet a finished dashboard you can optimize point by point, and anyone selling them that way is ahead of the evidence.
Suggested read: NAD Benefits: What Research Actually Shows
What this means for you day to day
You don’t need to think about methylation to act on this. The practical reading of the whole biological-age literature is simple: the inputs that keep your clocks slow are the same inputs that keep you healthy and alive. There’s no special “anti-aging” routine separate from the basics — the basics are the anti-aging routine.
So rather than chasing a number, put your energy into the inputs. Move daily, build some strength, eat mostly plants, protect your sleep, keep your stress in check, and stay connected to people. Do that for years and your biological age tends to take care of itself, test or no test.
Should you buy a biological-age test?
Consumer epigenetic-age tests are now widely sold, and they can be interesting. A few caveats before you spend:
- They’re estimates, not diagnoses. Results vary between labs and clocks
- Test-retest reliability differs by clock — pace-of-aging measures like DunedinPACE were specifically designed for better reliability
- A single number won’t tell you what to change — the lifestyle advice is the same regardless of your score
- Don’t let a “good” result make you complacent or a “bad” one panic you
If you find a test motivating, fine. But you already know what moves the needle, and you don’t need a kit to start.
Bottom line
Biological age is how old your body acts, not how old your ID says you are — and unlike your birthday, it’s partly in your hands. Epigenetic clocks like Horvath, GrimAge, and DunedinPACE estimate it from DNA methylation, with newer pace-of-aging tools acting like a speedometer for how fast you’re aging right now. A controlled trial has shown that lifestyle change can modestly slow that pace, but the effects are real-but-small, and no product reverses aging the way the ads imply. The reliable way to keep your biological age low is the same unglamorous list that predicts longevity: exercise, don’t smoke, eat mostly plants, sleep, manage stress, and stay connected. To go deeper on the cell-level story, see telomere health.
Horvath S. DNA methylation age of human tissues and cell types. Genome Biology. 2013;14(10):R115. PubMed | DOI ↩︎
Belsky DW, Caspi A, Corcoran DL, et al. DunedinPACE, a DNA methylation biomarker of the pace of aging. eLife. 2022;11:e73420. PubMed | DOI ↩︎
Waziry R, Ryan CP, Corcoran DL, et al. Effect of long-term caloric restriction on DNA methylation measures of biological aging in healthy adults from the CALERIE trial. Nature Aging. 2023;3(3):248-257. PubMed | DOI ↩︎ ↩︎
Aiello AE, Mishra AA, Martin CL, et al. Familial Loss of a Loved One and Biological Aging. JAMA Network Open. 2024;7(7):e2421869. PubMed | DOI ↩︎
