How large can the difference between my chronological age and my biological age be?

Your calendar age is simply how many years you have lived. Your biological age reflects how old your body looks on the inside. A large Chinese study with more than 12,000 participants combined 16 physical and 9 blood markers. The spread around the average difference was approximately 1.2 to 1.6 years. Individual outliers can be larger, but not a single study mentions a hard upper limit such as 'a maximum of 10 years'¹.

Review studies confirm that people age at very different rates. But exactly how large the difference can be depends on which measurement you use and which group you study^2,3,4. There is therefore no single answer.

Moreover, 'the' biological age is not a single number. Within one person, your liver, kidneys, immune system and metabolism can each age at their own pace⁵. Your biological age based on blood values can therefore differ from that based on a liver or kidney measurement.

What these measurements can do: predict health risks better than your year of birth. In a study with 9,389 participants and 18 years of follow-up, biological age predicted death considerably better than year of birth. Once biological age was included in the model, calendar age added barely anything⁶. A model combining blood values, proteins and metabolic markers showed the same thing: biologically older people had a significantly higher chance of chronic disease and earlier death⁷.

Epigenetic clocks, which work with the on and off switching patterns in your DNA, are a different approach. They correlate with disease and mortality, but can differ considerably from one another. Good comparative studies are still lacking³. For you as a consumer this means: two biological age tests can give a different number, even if you take them on the same day.