What's
your number?
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.
Drag the sliders. Watch your number change.
This is an estimate from the Rockport / Jackson equations. The real thing is measured breath‑by‑breath on a mask, and it's almost always different.
Estimate your VO₂ max.
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.
non‑exercise
equation ↓
The age your body thinks it is.
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.
HUNT study
n=4,637 ↓
What the number buys you.
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.
Mandsager
et al. ↓
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.
Translate it into a heart‑rate plan.
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.
+ Coggan
zones ↓
Eat the right amount of food.
RMR is your body's idle burn — 60–70% of total daily calories. Get it wrong by 300 kcal and twelve weeks later you're down 8 lb you didn't want to lose, or up 8 lb you didn't want to gain.
(estimate) ↓
Where these numbers come from.
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.
Jackson non‑exercise equation
Predicts VO₂ max from age, sex, BMI, and self‑reported activity. SEE ≈ 5.4 ml/kg/min vs. measured.
HUNT Fitness Study
n=4,637. Maps VO₂ max to population norms to derive "fitness age" — the age at which your VO₂ is median.
Cooper Institute cohort
n=122,007, 8‑yr follow‑up. All‑cause mortality hazard ratios by cardiorespiratory fitness quartile.
Tanaka formula
HRmax = 208 − 0.7 × age. Replaces the older 220−age with better validation across age groups.
Mifflin–St Jeor equation
Most accurate predictive equation for resting metabolic rate (within ±10% of indirect calorimetry).
ACSM reference values
VO₂ max percentiles stratified by age and sex. Industry‑standard reference for fitness classification.
Now get the real one.
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
- 12–18 min graded test on treadmill, bike, rower, or stair mill
- Ventilatory thresholds (VT1 / VT2)
- Personalized 5‑zone heart‑rate chart
- Same‑day results review with exercise physiologist
RMR
- 20‑min resting measurement, fasted
- Measured kcal/day — not estimated from formulas
- Fat‑vs‑carb fuel mix at rest
- Intake bands for cut / maintain / surplus
Full assessment
VO₂ max + RMR + body composition + a 30‑min debrief. The complete picture in 90 minutes.
Ninety minutes.
One number that will change
how you train for the next ten years.