Fitness Age & VO2max Calculator

What VO2max is, and why it matters

VO2max is the maximum amount of oxygen your body can use during hard exercise, measured in millilitres per kilogram of bodyweight per minute (ml/kg/min). It is the best single measure of cardiorespiratory fitness, and one of the strongest predictors of all-cause mortality: higher fitness tracks with a longer, healthier life. A true VO2max needs a lab test with a mask and a treadmill, while this tool estimates it instead from things you already know.

Why resting heart rate (and the face-age scan)

A lower resting heart rate generally reflects a stronger, more efficient heart, which is why the HUNT model uses it as an input [1]. It is not the biggest driver (your age, body composition and especially how hard you train matter more), but it sharpens the estimate. Don't know your resting heart rate? Our face-age scan can estimate it from your webcam in about 60 seconds and carry it into this calculator.

How accurate is a non-exercise estimate?

The HUNT model explains roughly 56 to 61% of the variation in measured VO2max, with a standard error of about 5 to 6 ml/kg/min [1, 2]. That is close to other non-exercise equations and good enough to place you in a fitness band, but not a substitute for a lab test. It tends to overestimate fitness in inactive people and underestimate it in well-trained athletes, so read your result as an orientation, not a verdict. This calculator uses the height-and-weight (BMI) variant [2], which is about as accurate as the original waist version [1].

How to move the number

VO2max is responsive to training in general. In the research, the inputs most associated with a higher estimate are training intensity (sessions hard enough to leave you breathing heavily) and a mix of easy aerobic volume with short, hard intervals over weeks to months; a lower body-fat level around the middle and a lower resting heart rate are also associated with higher values. What works for any individual is best discussed with a doctor or a qualified coach.

What is a good VO2max for your age?

These are the average (50th-percentile) VO2max values measured on a treadmill in healthy adults, by age and sex (FRIEND registry [3]). Landing above your row is above average for your age; below it is below average.

Values in ml/kg/min. Your own estimate above is placed on the full percentile range, not just this midpoint.

Where your percentile comes from

The FRIEND registry publishes one VO2max value at the 5th, 10th, 25th, 50th, 75th, 90th and 95th percentile for every ten-year age band, separately for men and women, all measured on a treadmill in a clinical exercise lab [3]. The table above prints the 50th-percentile column of that grid. Your own number is placed between those anchors by straight-line interpolation, so a value halfway between two of them reads as a percentile halfway between them, and a value beyond the outermost anchor is extended gently instead of being pinned at the 5th or the 95th. The five fitness labels come from cutting that percentile at 20, 40, 60 and 80; those edges are the ACSM category overlay, not part of the FRIEND data. Ages under 20 and over 79 sit outside the published tables, so they are compared with the nearest band and the result card says so.

What is fitness age, and how is it calculated?

Fitness age asks a different question than your birthday does: at what age would your VO2max be an average result? We calculate it with the linear mapping published by the NTNU group [5], the same one their own calculator uses. For men it is 160.7 minus 2.513 times your VO2max; for women it is 155.8 minus 3.049 times your VO2max. The result is rounded, never drops below 20, and stops at 80 below age 70 or at 90 from age 70. Two worked examples: a man with a VO2max of 42 ml/kg/min gets 160.7 - (2.513 × 42) = 55.2, a fitness age of 55; a woman with 34 gets 155.8 - (3.049 × 34) = 52.1, a fitness age of 52. Watch which reference sits behind which number: this mapping is calibrated on the healthy Norwegian HUNT cohort, while the percentile and the fitness level next to it are graded on the US FRIEND registry [3]. The fitness age beside it uses the Norwegian reference, so the two will disagree. If you wear a smartwatch you have probably met this number under another name: Apple Watch calls it Cardio Fitness, Garmin reports VO2 max, Fitbit shows a Cardio Fitness Score, and all three describe the same quantity this page estimates. They derive it from your heart rate and pace during exercise, while this calculator derives it from a resting heart rate and a self-reported training week with no exercise at all, so the numbers will not match exactly. If you already have a value from a watch or a lab test, enter it directly in the calculator above instead of estimating a new one.

The HUNT equations this calculator uses

This calculator uses the HUNT BMI model (Nes et al. 2011 [1]), printed in Jalene et al. 2019 [2]. VO2max is in ml/kg/min, AGE is age in years, BMI is body mass index in kg/m² (weight in kg divided by height in metres squared), RHR is resting heart rate in beats per minute, and PA is the HUNT physical-activity index, which this calculator derives from your typical training week rather than asking for it directly. Men (R² = 0.59, SEE = 5.8 ml/kg/min): VO2max = 92.05 - (0.327 × AGE) - (0.933 × BMI) - (0.167 × RHR) + (0.257 × PA). Women (R² = 0.57, SEE = 5.1 ml/kg/min): VO2max = 70.77 - (0.244 × AGE) - (0.749 × BMI) - (0.107 × RHR) + (0.213 × PA). SEE is the standard error of the estimate, in ml/kg/min. The waist-circumference variant of the same model is a separate fit with its own coefficients, and this calculator does not use it.

How this compares to NTNU's World Fitness Level calculator

Both calculators run the same non-exercise model from the HUNT study [1]. NTNU's World Fitness Level calculator [5] is that model's original deployment; this page is a separate implementation of the published equations, not a partner site and not an official version of theirs. Three things differ in practice. First, the body input: theirs takes waist circumference, this one takes height and weight, which is a separately fitted version of the same model with its own coefficients [2]. Second, the activity question: theirs asks how long a typical session lasts, while this one holds session length at the neutral midpoint and reads frequency and intensity off your training week, so the activity index can land a little above or below theirs. Third, the reference population behind the verdict: the fitness level here is graded on the US FRIEND registry [3], theirs against a Norwegian reference, so the same VO2max can be described in different words. The fitness age is the one number on this page that stays on the Norwegian reference, which is why it can disagree with the level beside it.

Frequently asked questions

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