There is more than one way to calculate biological age.
Different methods use clinical and biological information in different ways. This means that two methods applied to similar health data may not measure exactly the same aspect of biological aging.
Three established approaches used in biological-aging research are KDM Biological Age, PhenoAge and Homeostatic Dysregulation.
KDM Biological Age
The Klemera–Doubal Method (KDM) combines information from multiple biomarkers and examines how they relate to chronological age.
The result is expressed in years. A person's KDM Biological Age can therefore be higher or lower than their chronological age.
In simple terms, KDM looks at how a person's biomarker profile compares with age-related patterns observed in a reference population.
PhenoAge
PhenoAge takes a different approach.
It combines clinical biomarkers and chronological age using a model developed around mortality risk. The result is then expressed as an age-equivalent value.
This means that PhenoAge is designed to capture information related not only to age, but also to differences in health and mortality risk.
Homeostatic Dysregulation
Homeostatic Dysregulation (HD) looks at biological aging from another perspective.
Rather than primarily producing an age in years, it measures how far a person's combined physiological profile differs from a healthy reference profile.
A greater difference indicates greater physiological dysregulation.
Why Do These Differences Matter?
A biological-age result is not determined by biomarkers alone. It also depends on the method used to combine and interpret them.
KDM Biological Age, PhenoAge and Homeostatic Dysregulation illustrate this particularly well. They can use clinical biomarker information but approach biological aging from different perspectives: age-related change, mortality-related risk, or physiological dysregulation.
Knowing which method was used therefore helps us understand what a biological-age result actually represents.
