PhenoAge, Bortz or an epigenetic clock: which biological age test is worth it?

Biological age estimates how old your body behaves, rather than how many birthdays you've had. Two people born on the same day can be biologically years apart, and unlike your calendar age, the biological one responds to how you live. There are three main ways to measure it.

1. Blood-based clocks: cheap, repeatable, the place to start

PhenoAge (2018) combines your age with nine markers from a standard blood panel: albumin, creatinine, glucose, C-reactive protein, lymphocyte percentage, mean cell volume, red-cell distribution width, alkaline phosphatase and white blood cell count. It predicts mortality considerably better than age alone.

The Bortz clock (2023) was trained on around 300,000 people in UK Biobank using a wider set of routine blood markers. It improved on PhenoAge's prediction by about 11 %. Its single most informative marker was cystatin C, a kidney marker most panels leave out.

Both can be calculated from results you may already have, using free online calculators. Cost: whatever the blood panel costs, roughly €30–150. They're also what the Longevity World Cup uses to rank competitors: PhenoAge for its amateur track and Bortz for its professional track in 2026.

2. Epigenetic clocks: more sophisticated, more expensive, noisier

These read DNA methylation, chemical tags on your DNA that shift with age and lifestyle.

• Horvath's clock (2013) was the first.
• GrimAge (2019) is one of the best predictors of lifespan.
• DunedinPACE (2022) estimates your pace of ageing, in biological years per calendar year, and is the most sensitive to change.

Consumer epigenetic tests cost around €200–500. Their weakness is reliability: the same sample run twice can give results years apart with some clocks, and different companies use different methods. Newer approaches reduce the noise, but they're still best read as a trend, from the same lab, once a year.

3. Functional age: free, and surprisingly powerful

VO2 max, grip strength, the sitting-rising test, balance and walking speed each predict mortality on their own. Compare your results with the norms for your age and you have a functional age without any lab.

Which one should you use?

• Functional age first. It's free, and it points at things you can train.
• A blood clock when you have a panel. Once you reach the Advanced level, you'll have most of the markers anyway.
• An epigenetic test only if you're curious and at the Optimized level. Same lab, once a year, trend only.

And measure last, not first. If your waist, blood pressure and fitness are off, you already know which way your biological age points. Fix those, then test, and enjoy watching the number come down.

In the journal: biological age is an Optimized box, page 11. The course chapter on biological age goes deeper.

Sources: Levine et al., Aging 2018 · Bortz et al., Communications Biology 2023 · Lu et al., Aging 2019 · Belsky et al., eLife 2022 · Higgins-Chen et al., Nature Aging 2022.