In this guide
Quick answer: chronological age is the time since you were born. Biological age is an estimate of how well your body is functioning compared with others of your age.
Chronological age
Chronological age is counted in years, months and days from your date of birth. It is fixed and exact, and it is the age used on official documents, in schools and sports, and for legal purposes. You can find yours with the age calculator.
Biological age
Biological age, sometimes called physiological age, tries to describe how old your body seems based on measurements rather than the calendar. Two people with the same birthday can differ a lot: one may have the fitness and blood markers typical of someone younger, another those typical of someone older.
How biological age is estimated
- Epigenetic clocks use patterns of chemical marks on DNA. The first widely known clock was published in 2013.
- Blood biomarkers such as cholesterol, blood sugar and inflammation markers can be combined into a score.
- Fitness measures like grip strength, walking speed and how quickly your heart recovers after exercise also reflect aging.
How reliable are the results?
Research on these measures is active, and results from different tests often disagree with each other. Consumer tests vary in quality, and a biological age number is not a diagnosis. It is best read as a rough guide to trends, ideally discussed with a doctor.
What affects biological age?
Factors linked with healthier aging include regular physical activity, not smoking, a balanced diet, healthy sleep and staying socially connected. Genetics, income and environment also play a part, and many of them are outside your control.
Which one should you use?
Use chronological age for anything official or exact. Treat biological age as a curiosity, or as a prompt to look at habits such as sleep and weight, and check the adult BMI range with the BMI calculator.
This guide is general information, not medical advice. Speak to a doctor about your own health.
Try the calculators
- Age Calculator by Date of Birth: Exact age, total days lived, next birthday
- Sleep Calculator: Bedtime and wake-up times by sleep cycles
- BMI Calculator: Body mass index and healthy range
General information only, not professional advice. See our editorial policy.