What is biological age and how can it be measured?

In brief: The term 'biological age' refers to the extent of the ageing process in the body. At present, this cannot be measured accurately using a single test. Researchers instead use various methods, such as epigenetic clocks, blood markers, telomere length and physical or cognitive tests. While these methods provide valuable insights into the ageing process, they are not yet established as diagnostic tools for individuals.

When asked about their age, people usually quote their chronological age, i.e. the number of years since their birth. However, this figure only provides limited insight into the body’s actual condition. It is possible for two people of the same chronological age to differ significantly in terms of their physical condition and health: while one 50-year-old can still run a marathon, another might already be exhausted just from climbing stairs.

Biological age describes how far biological ageing processes have progressed in the body. However, there is no single biological age. Different organs and tissues can age at different rates. Therefore, the biological age of the brain, heart, or kidneys may differ from that of other parts of the body. These organ-specific ageing profiles are an important area of research but are not yet an established diagnostic tool for individuals (Oh HS et al., 2023).

Various approaches exist for measuring biological age or age-related changes:

Epigenetic tests: These tests measure chemical changes to DNA, known as DNA methylation patterns, which change with age. On this basis, so-called epigenetic clocks have been developed (see the FAQ 'What is the epigenetic clock?' for more information).
Telomere length: Telomeres are protective caps at the ends of chromosomes that shorten with each cell division. Their length has therefore been investigated as a potential marker of ageing processes. However, as telomere length varies greatly from person to person and is influenced by many factors, it provides only limited information about biological age on its own (Bekaert S et al., 2005; Mather KA et al., 2011).
Markers in blood and other bodily fluids: Certain measurable values in blood or other bodily fluids can indicate age-related changes. These include inflammatory markers, metabolic parameters such as glucose or insulin levels, and markers of the immune system (Jylhava et al., 2017). The Deelen research group at the Max Planck Institute for Biology of Ageing investigated the relationship between metabolomics and life expectancy, identifying a set of 14 metabolic markers (Deelen et al., 2019). Additionally, there are so-called 'proteomic ageing clocks', which are based on measuring protein levels in bodily fluids (Argentieri MA et al., 2024; Rutledge J et al., 2022).
Physiological tests: These tests assess the function of various organs and bodily systems, such as lung capacity, blood pressure, vision and hearing, cardiovascular fitness, muscle strength, and joint mobility.
Cognitive tests: These tests evaluate different aspects of cognitive function, such as memory, attention, problem-solving ability, and processing speed.

As ageing is a complex process, using a combination of measurement methods is likely to provide the most comprehensive information. This allows different levels of ageing to be taken into account.

Many measurement methods, such as epigenetic or proteomic clocks, are based on large datasets and statistical correlations with age, disease risk or survival. These methods are highly valuable in research, providing important insights into age-related changes. However, caution should be taken when interpreting individual test results, as different tests capture different aspects of the ageing process, and results may depend on the specific method and context. While commercial tests can provide interesting information, they should not be regarded as the sole basis for medical or health-related decisions.

Unfortunately, we are unable to determine the biological age of individuals at the Max Planck Institute for Biology of Ageing. Our research focuses on fundamental scientific questions. To this end, we use samples from clinical trials or data from biobanks, amongst other things. We do not carry out tests on private individuals.

Updated on July 2nd 2026