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Two measurements tell you more about how long you'll live well than anything on your wrist. Play with them below — then come find out your real one.
Estimate uses the Jackson non-exercise equation (BMI form, 1990); percentile and fitness age use the FRIEND registry norms (Kaminsky 2015). The real thing is measured breath-by-breath on a mask and it's almost always different.
Self‑reported inputs get you into the right ballpark. A graded test on a metabolic cart gets you the real number — usually within 1 ml/kg/min of truth.
A VO₂ max of 42 at age 55 is a very different story than the same 42 at age 28. Fitness age translates your number into years.
In the Cooper Institute cohort (n=122,007, 8‑year follow‑up), moving from the bottom quartile to above‑average cut all‑cause mortality in half. This is a bigger effect than quitting smoking.
Top quartile. Hold it. Every additional 1 ml/kg/min above this still reduces risk — but you're past the cliff.
Reduction in all‑cause mortality risk, holding everything else equal. That's the leverage of a single METs improvement.
A measured VO₂ max test in Santa Cruz puts a real number on this chart. Same-day report, training zones included. $250 — or $50 to hold a slot.
A 12-page plain-language PDF. Your numbers, decoded — zones, thresholds, and what to do next.
Zones derived from max HR are educated guesses. Zones derived from ventilatory thresholds are prescriptions. Here's the guess — the test gives you the prescription.
The estimators on this page are validated equations from the published literature. They get you close — a measured test gets you the real thing. Here's every source we use, so you can check our work.
Predicts VO₂ max from age, sex, BMI, and self‑reported activity. SEE ≈ 5.4 ml/kg/min vs. measured.
n=4,637. Maps VO₂ max to population norms to derive "fitness age" — the age at which your VO₂ is median.
n=122,007, 8‑yr follow‑up. All‑cause mortality hazard ratios by cardiorespiratory fitness quartile.
HRmax = 208 − 0.7 × age. Replaces the older 220−age with better validation across age groups.
VO₂ max percentiles stratified by age and sex. Industry‑standard reference for fitness classification.
Estimates are fine. A graded test on a metabolic cart takes 45 minutes and gives you measurements accurate to within 1%. You leave with personalized zones and intake targets the same day.
VO₂ max + RMR + body composition + a 30‑min debrief. The complete picture in 90 minutes.