Your race times already contain a fitness test. Enter a recent 5K, 10K, half, or marathon and we'll estimate your VO2max, then tell you the age your cardiorespiratory fitness actually matches — benchmarked against real treadmill data from thousands of people.
Your details
A recent race & you
We estimate your VO2max from the race with Jack Daniels' VDOT, then find the age it's typical for — using FRIEND registry reference data. Nothing leaves your browser.
Your running fitness age
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Enter your age and a recent race result to see the age your fitness matches.
The middle-of-the-pack (50th-percentile) VO2max at each age, from the FRIEND registry of directly measured treadmill tests. Your fitness age is the row your own estimate lands on. Beating the number for your decade means your fitness age is younger than your real one.
| Age group | Men (ml/kg/min) | Women (ml/kg/min) |
|---|---|---|
| 20–29 | 48.0 | 37.6 |
| 30–39 | 42.4 | 30.2 |
| 40–49 | 37.8 | 26.7 |
| 50–59 | 32.6 | 23.4 |
| 60–69 | 28.2 | 20.0 |
| 70–79 | 24.4 | 18.3 |
Source: Kaminsky LA et al., Reference Standards for Cardiorespiratory Fitness, Mayo Clinic Proceedings, 2015.
Step 1 — VO2max from your race
VDOT = VO₂(pace) ÷ %VO₂max(duration)
Jack Daniels' VDOT model turns a race result into an effective VO2max. It reads your velocity and how long you held it, then solves for the aerobic power that performance required. Because it uses a real maximal effort, it's far more accurate for runners than any lifestyle questionnaire.
Step 2 — match it to an age
fitness age = age where median VO₂max = yours
We compare your VO2max to sex-specific 50th-percentile norms from the FRIEND registry and read off the matching age. VO2max falls about 9–10% per decade on average, so being well above your decade's median translates to a fitness age several years younger.
The estimate assumes your race was a genuine, well-paced maximal effort on a fair course. Heat, hills, a blow-up, or an easy day will all pull the number around — treat it as a solid benchmark to track over time, not a lab measurement.
It predicts longevity
Cardiorespiratory fitness is one of the strongest single predictors of all-cause mortality — often stronger than smoking status, blood pressure, or cholesterol. A lower fitness age is a proxy for a lower long-term health risk.
It responds to training
Unlike your calendar age, this one moves. Consistent aerobic base work plus a weekly hard session raises VO2max at any age, and the fitness-age drop is visible within a couple of training blocks.
It makes a number click
"VO2max 48" means little day to day. "Fitness of a 30-year-old" is a goal you can feel. Reframing the physiology as an age is what makes it stick.
Fitness age is your cardiorespiratory fitness expressed as an age. We estimate your VO2max from a recent race, then find the age at which that VO2max is the typical, middle-of-the-pack value. If a 50-year-old has the VO2max normally seen in 40-year-olds, their fitness age is 40 — ten years younger than the calendar says. It reframes an abstract number (VO2max in ml/kg/min) as something intuitive.
Two steps. First we estimate your VO2max from your race time and distance using Jack Daniels' VDOT formula, which is well validated across 1500m to the marathon. Then we compare that value against 50th-percentile VO2max norms by age and sex from the FRIEND registry — a large database of directly measured treadmill fitness tests — and read off the age your fitness matches. Your chronological age is used only to show the gap and your percentile, never to compute the fitness age itself.
Many fitness-age tools estimate VO2max from a lifestyle questionnaire because they assume you haven't done a fitness test. As a runner, you have — every race is a maximal test. A real performance gives a far more accurate VO2max than answering questions about how active you feel, so we ask for your best recent effort at a distance instead.
Use a recent, genuinely hard effort. A 5K or 10K raced flat-out is ideal because it's close to VO2max intensity and less affected by pacing, fuelling, and heat than a marathon. If you enter a marathon, make sure it was well paced — a blow-up in the final 10K will understate your true fitness. The result is only as good as the effort behind it.
A lower fitness age means better aerobic fitness for your years, which is strongly linked to lower risk of heart disease and death — so directionally, yes. But it's one measure, not a verdict on health. Strength, mobility, body composition, sleep, and stress all matter too, and a single race can be thrown off by a bad day. Treat it as a motivating benchmark to move over time, not a diagnosis.
They're the same information in two languages. VO2max is the raw physiological number — how much oxygen your body can use per kilogram per minute. Fitness age translates that number onto the age scale by asking 'whose typical VO2max is this?' VO2max is what sports scientists measure; fitness age is what makes it click for the rest of us.
Raise your VO2max, and consistency beats intensity. Build a base of easy aerobic running (most of your weekly volume should feel conversational), add one or two harder sessions a week — think 3–5 minute intervals at hard effort or a sustained tempo — and stay patient. VO2max is one of the most trainable numbers in the body: meaningful gains show up in 8–12 weeks of steady work, at any age.
GPS watches estimate VO2max from your heart rate and pace on every run, then smooth it over weeks; we estimate it from one maximal race using a published formula. Watches can drift if your heart-rate data is noisy or your max heart rate is set wrong, and they lean on models too. Expect them to be in the same neighbourhood, not identical — a race-based estimate is usually the more reliable of the two.