How Bio Age works
Last updated November 9, 2026
Bio Age in Hush is a fitness age: the age whose typical cardio fitness matches yours. It is a wellness estimate based on one measure, cardio fitness (VO2 max). It is not a medical test and it does not measure your cells, your health or how long you will live.
The calculation
Hush reads your latest VO2 max estimate from Apple Health. It then finds the age at which the published median VO2 max for your sex equals yours, moving in a straight line between the middle of each age decade.
| Age | Women | Men |
|---|---|---|
| 20 to 29 | 36.6 | 46.5 |
| 30 to 39 | 28.3 | 39.7 |
| 40 to 49 | 25.7 | 35.3 |
| 50 to 59 | 22.9 | 29.2 |
| 60 to 69 | 19.6 | 24.6 |
| 70 to 79 | 17.2 | 20.6 |
| 80 to 89 | 15.4 | 17.6 |
Values are 50th percentile treadmill VO2 peak in mL/kg/min from the FRIEND registry. Bio Age needs a VO2 max reading and your sex at birth, because the published tables are separate for women and men.
What to keep in mind
- Apple Watch VO2 max is an estimate. In Apple's validation it averaged 1.4 mL/kg/min above reference, with a standard deviation of 4.7. An independent study of mostly fit adults found it read lower than lab testing by about 6 mL/kg/min. Either can move your Bio Age by years.
- Medications that limit heart rate can affect the reading.
- Bio Age reflects cardio fitness only.
- Check with a doctor before making medical decisions.
Sources
- Kaminsky LA, et al. Updated Reference Standards for Cardiorespiratory Fitness Measured with Cardiopulmonary Exercise Testing: FRIEND. Mayo Clinic Proceedings, 2022. doi.org/10.1016/j.mayocp.2021.08.020
- Apple. Using Apple Watch to Estimate Cardio Fitness with VO2 max, 2021, which uses the FRIEND registry for its age and sex thresholds. Apple white paper
- Nes BM, et al. A simple nonexercise model of cardiorespiratory fitness predicts long-term mortality. Medicine and Science in Sports and Exercise, 2014, the fitness age research from NTNU. PubMed
- Lambe R, O'Grady B, Baldwin M, Doherty C. Investigating the accuracy of Apple Watch VO2 max measurements: a validation study. PLOS ONE, 2025. Full text