Methodology
How the biological age estimate works
What it is
An estimate of your biological age, worked out from a questionnaire about your day-to-day habits and compared with people your age in large population studies. It is shown as a range of plus or minus two years because no questionnaire can be exact.
What it is not
It is not a lab measurement of biological age, and it is not a medical test. A lab-based estimate comes from blood or DNA markers, such as the blood and epigenetic tests in a wellness consultation, and even those tests carry real uncertainty. Nothing in your result diagnoses, treats or prevents any condition.
How the years are worked out
Each factor's contribution is derived from hazard ratios in large prospective cohort studies, converted to years using the 'effective age' method (years ≈ 10 × ln of the hazard ratio), then reduced to allow for overlap between factors and cross-checked against studies that used blood or DNA-based measures of biological age. The total is capped at 6 years younger to 12 years older. Concerns you report are shown as discussion points and do not change the estimate.
For anyone under 30 the effects are halved, because most of the research was done in people over 40. Smoking is the only factor that can push an estimate more than eight years above calendar age.
| Factor | Range | Evidence |
|---|---|---|
| Smoking | 0 to +6 years | Strong |
| Physical activity | −2 to +2.5 years | Strong |
| Body weight (BMI) | −0.5 to +4 years | Strong |
| Diet | −1.5 to +1.5 years | Moderate |
| Sleep | −0.5 to +2 years | Moderate |
| Alcohol | 0 to +2 years | Moderate |
| Stress | −0.5 to +1.5 years | Early |
| Social connection | −0.5 to +1 year | Early |
What doesn't count
Symptoms such as tiredness, brain fog or skin changes do not move your estimate. No study links them to biological age, and each has several ordinary medical causes that deserve a proper check. We show them in your report as things to discuss, with the tests a clinician would usually consider.
The limits
The studies are observational: they show what tends to be true across many thousands of people, not what will happen to you. Answers are self-reported. BMI cannot tell muscle from fat. And a questionnaire cannot see your blood pressure, blood sugar, cholesterol or family history, which matter at least as much.
Can the number be changed?
Randomised trials show that lifestyle changes produce small, measurable shifts in DNA-based ageing markers: about 2–3% slower pace of ageing after two years of calorie restriction, and a few months' difference over three years with omega-3, vitamin D and exercise. Those are real but modest effects, and no trial has shown that changing such a marker makes people live longer. We don't promise to change yours.
Sources
- Li Y, et al. Impact of healthy lifestyle factors on life expectancies in the US population. Circulation 2018;138:345-355.
- Nguyen XT, et al. Impact of 8 lifestyle factors on mortality and life expectancy among US veterans: the Million Veteran Program. Am J Clin Nutr 2024;119:127-135.
- Jha P, et al. 21st-century hazards of smoking and benefits of cessation in the United States. N Engl J Med 2013;368:341-350.
- Global BMI Mortality Collaboration. Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies. Lancet 2016;388:776-786.
- Kusters CDJ, et al. Short sleep and insomnia are associated with accelerated epigenetic age. Psychosom Med 2024.
- Alcohol consumption and epigenetic age acceleration across human adulthood (Framingham Heart Study). Aging 2023.
- Harvanek ZM, et al. Psychological and biological resilience modulates the effects of stress on epigenetic aging. Transl Psychiatry 2021;11:601.
- Holt-Lunstad J, Smith TB, Layton JB. Social relationships and mortality risk: a meta-analytic review. PLoS Med 2010;7:e1000316.
- Spiegelhalter D. How old are you, really? Communicating chronic risk through 'effective age' of your body and organs. BMC Med Inform Decis Mak 2016;16:104.
- Zhang H, et al. Association between Life's Essential 8 and biological ageing among US adults. J Transl Med 2023;21:622.
- Zhang et al. Lifestyles and their relative contribution to biological aging across multiple-organ systems: the China Multi-Ethnic Cohort study. eLife 2025;13:RP99924.
- Waziry R, 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;3:248-257.
- Bischoff-Ferrari HA, et al. Individual and additive effects of vitamin D, omega-3 and exercise on DNA methylation clocks of biological aging in older adults from the DO-HEALTH trial. Nature Aging 2025.
This is an educational estimate, not a medical test. It converts your answers into years using published associations between lifestyle and health outcomes in large population studies. Those studies describe averages across thousands of people and cannot predict an individual's health. Biological age can only be measured from blood or DNA biomarkers, and even those tests carry measurement uncertainty. This tool does not diagnose, treat or prevent any condition. Speak to a GP about any symptoms.
Take the questionnaire →