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Interactive tool · Cardiorespiratory fitness

Fitness Age & VO2max Estimator

VO2max — the most-studied single marker of cardiorespiratory fitness — is one of the strongest predictors of all-cause mortality, yet almost no one has it measured in a lab. This tool estimates it without exercise, from the same everyday inputs the HUNT study used — your age, sex, waist, resting heart rate and weekly activity — and translates the number into a plain-language “fitness age.” It is an estimate from a population model, not a measurement.

Read before you use this

This is an educational estimate, not a medical assessment. It is not a clinical VO2max test — true VO2max is measured in a lab with a graded treadmill or cycle protocol and a gas analyzer, and a non-exercise model like this one carries an error of several mL/kg/min for any individual. Cardiorespiratory fitness is one of many longevity factors, and a “fitness age” is a motivational translation, not a diagnosis. If you have heart disease, chest pain, uncontrolled blood pressure, or other risk factors, talk to a clinician before starting or intensifying exercise. Treat every number below as a rough starting point, not a result.

Which model this is — in plain terms

The peer-reviewed HUNT non-exercise model (Nes et al., 2011) estimates VO2peak from exactly the inputs we ask for — sex, age, waist circumference, resting heart rate, and leisure-time physical activity — and explains roughly 61% and 56% of the variance in men and women. We could verify the study and its variables, but its exact regression coefficients sit behind a paywall, so rather than print numbers we could not confirm, this calculator uses a transparent, openly-stated heuristic built on the same variables and calibrated to the published mean-VO2max-by-age values from NTNU/CERG (the group behind the HUNT calculator). The age term tracks those averages closely; the waist, resting-HR and activity adjustments are modest, directionally-correct terms — not validated effect sizes. So this is a defensible heuristic, not the exact validated equation. Honesty over false precision.

Sex at birth
The HUNT model is sex-specific; the average-fitness curve differs for men and women.
Waist circumference
Measure around the navel, relaxed. Waist (not BMI) is the body-size term in this model.
Weekly physical-activity level
~1–2 sessions a week. Mirrors the leisure-time activity index in the HUNT model.

Estimated VO2max

48.4mL/kg/min

Average for a 40-year-old man is about 48.4. You are average for your age (+0 mL/kg/min).

Estimated fitness age

40yr

Your fitness is close to average for your chronological age.

Estimated VO2max
48.4 mL/kg/min
non-exercise estimate
Average for your age
48.4 mL/kg/min
CERG mean by age & sex
Difference
+0 mL/kg/min
average

How it is calculated. We use the same inputs as the HUNT non-exercise model — sex, age, waist, resting heart rate, and leisure-time activity — in a transparent, sex-specific line whose age term is calibrated to the published NTNU/CERG mean-VO2max-by-age values; waist, resting-HR and activity then nudge the estimate up or down. Fitness age is read back off the same average curve: the age at which your estimated VO2max would be average. Worked example: a reference 40-year-old man (waist 94 cm, resting HR 60, “Some” activity) estimates to 48.4 mL/kg/min, which is exactly average for age 40 — so his fitness age reads 40. This is a heuristic, not the exact published regression coefficients — see the note above the tool.

Put the number in context

An estimate is only useful if you know what to do with it. These cover why VO2max matters for lifespan, how to actually raise it, and how it sits alongside other longevity markers:

Reference

Nes BM, Janszky I, Vatten LJ, Nilsen TI, Aspenes ST, Wisløff U. Estimating V̇O2peak from a nonexercise prediction model: the HUNT Study, Norway. Med Sci Sports Exerc. 2011 Nov;43(11):2024–30. PMID 21502897. Mean-VO2max-by-age reference values: NTNU/CERG “Fitness numbers.” This calculator implements an openly-stated heuristic built on this model's variables and calibrated to those published averages, not the paper's exact regression coefficients.

This calculator is informational and not medical advice. It produces a population-model estimate of cardiorespiratory fitness and does not account for your individual health history, medications, or conditions. It is not a clinical VO2max test and not a diagnosis. Consult a licensed clinician before starting or changing an exercise program, especially if you have cardiovascular risk factors.