Why Different Biological Age Tests Give Different Results
Different training targets and measurements can produce different answers from the same person.
AI-assisted editorial draft · Source check: 6 September 2026 · Independent reviewer: not yet assigned
There is no single shared scale
A blood composite, a methylation clock and a glycan model observe different signals. Some are calibrated to age; others use outcome associations or longitudinal change. Matching units on the report do not make the underlying models identical.
Source 1: PLOS Medicine / Liu et al.Source 2: Genome Biology / HorvathSource 3: Journals of Gerontology / Krištić et al.Source 4: eLife / Belsky et al.Record what actually changed
When retesting, keep a note of the provider, sample type, assay, model version and collection conditions. If several of those change at once, you cannot confidently attribute a new score to a lifestyle change.
Read changes cautiously
For a trend, use the same provider and method where possible, and check whether the algorithm has changed. Avoid averaging unrelated age scores into a supposed definitive age. Discuss worrying clinical laboratory results with a qualified clinician.
Sources & verification
- A new aging measure captures morbidity and mortality risk (2018)
PLOS Medicine / Liu et al. · Accessed 2026-09-06
- DNA methylation age of human tissues and cell types (2013)
Genome Biology / Horvath · Accessed 2026-09-06
- Glycans are a novel biomarker of chronological and biological age (2014)
Journals of Gerontology / Krištić et al. · Accessed 2026-09-06
- DunedinPACE, a DNA methylation biomarker of the pace of aging (2022)
eLife / Belsky et al. · Accessed 2026-09-06