Fitbit VO2 max, which the Fitbit app called the Cardio Fitness Score until May 2026, is an estimate of the maximum oxygen your body can use during exercise, in millilitres per kilogram per minute, worked out from the relationship between your running pace and heart rate on GPS runs, compared against your resting heart rate. The Google Health app sorts the result into six levels, Poor, Fair, Average, Good, Very Good and Excellent, using published tables by age and sex, so a 42 is Average for a 25-year-old man and Excellent for a 45-year-old woman. This page covers how the estimate is made, the level tables, why the old range-without-running disappeared, how accurate the number is against a lab and against Apple Watch and Garmin, which devices support it, whether Premium matters and what actually raises it. For the recovery side of the same heart data, see Fitbit HRV explained.
The short version
You now need GPS runs to get a Fitbit VO2 max at all, the number is accurate to roughly 10 percent, and the three-month trend is the only view worth acting on. Google dropped the old demographic estimate when the Fitbit app became Google Health, so non-runners no longer see a range. Run outdoors for at least 10 minutes with GPS, on flat ground, up to three times in 30 days, and a single value appears under Key metrics in the Fitness tab. It is free on every Fitbit and Pixel Watch that can capture GPS, built in or from your phone. Raising it takes weeks of consistent running with some intensity; losing it takes only a few weeks off.
What VO2 max is and why Fitbit renamed the score
VO2 max is the ceiling on how much oxygen your heart, lungs and muscles can deliver and use per minute of hard exercise, scaled to body weight. It is the standard lab measure of cardiorespiratory fitness and one of the strongest predictors of endurance and long-term health; large cohort studies show low cardiorespiratory fitness carries a higher all-cause mortality risk than smoking or hypertension. The lab test is a treadmill or bike ramp to exhaustion with a mask measuring the gases you breathe. No wearable measures oxygen; all of them estimate VO2 max from the relationship between workload and heart rate.
Fitbit launched its estimate as the Cardio Fitness Score in 2017, a friendlier name for the same quantity. When the Fitbit app became the Google Health app on May 19, 2026, Google's release notes stated plainly that "Cardio fitness score will now be called VO2 max", and the metric screen in the app still carries the subtitle "formerly known as cardio fitness score". Anyone searching for "fitbit cardio fitness score" and "fitbit vo2 max" is looking for the same thing. Google's own definition is the amount of oxygen your body uses during exercise, and it describes VO2 max as a strong predictor of endurance, overall cardio health and longevity.
How Fitbit estimates VO2 max in 2026
Google's help page describes three steps. Running efficiency: during an outdoor run with GPS, the app tracks the ratio between your pace and your heart rate, which shows how hard your heart works to hold a given speed. VO2 max estimation: that efficiency is compared against your resting heart rate to produce the number; two people running 5:30 per kilometre at 150 and 170 beats per minute get different results, and the one whose resting heart rate is lower gets more credit. Fitness level: the value is then placed against benchmarks for your age and sex to give one of the six labels. Only outdoor running counts. Google is explicit that VO2 max is not measured while walking, cycling or on a treadmill, and that only GPS runs of at least 10 minutes feed it, with flat sections weighted because hills break the pace-to-heart-rate relationship.
Resting heart rate still matters, which is why wearing the device to sleep improves the estimate, but the old inputs of height and weight do not. Google's May 2026 notes say the score "will no longer be calculated based on your demographics, such as your height and weight", and that VO2 max can now also be calculated from runs synced by connected third-party apps. For the first value Google says one 10-minute run may be enough, but you may need up to three runs in 30 days. Faster runs give a better estimate; you do not need to run flat out, but higher intensity narrows the error.
Why the range disappeared
The most common old complaint, "why does my Fitbit show a range instead of a number", had a simple cause. In the Fitbit app, users who never ran with GPS received a broad range, typically spanning six or seven points, estimated from resting heart rate, age, sex, weight and profile data alone. Only after GPS runs did the app narrow it to a single figure. That fallback is gone. The Google Health app estimates VO2 max only during GPS runs, so a walker or cyclist who used to see a range now sees nothing until they log a qualifying run. It is a loss for non-runners but an honest one: the demographic range said very little about you. If you want a VO2 max without running, Apple Watch still estimates it from brisk outdoor walks as well as runs, and Garmin estimates it from cycling with a power meter; see HRV on Apple Watch explained for how Apple's heart metrics fit together.
The six cardio fitness levels by age and sex
Google publishes the full tables in its help centre. Values are VO2 max in ml/kg/min; each band runs from the lower figure up to the next band's lower figure.
| Age | Poor | Fair | Average | Good | Very good | Excellent |
|---|---|---|---|---|---|---|
| Men | ||||||
| 20 to 30 | under 36.8 | 36.8 | 42.7 | 48.6 | 54.6 | 60.4 and up |
| 30 to 40 | under 33.5 | 33.5 | 38.9 | 44.2 | 49.6 | 55.0 and up |
| 40 to 50 | under 30.2 | 30.2 | 35.0 | 39.8 | 44.6 | 49.4 and up |
| 50 to 60 | under 26.7 | 26.7 | 31.1 | 35.4 | 39.6 | 44.0 and up |
| 60 plus | under 23.4 | 23.4 | 27.2 | 31.0 | 34.7 | 38.7 and up |
| Women | ||||||
| 20 to 30 | under 31.2 | 31.2 | 35.9 | 40.8 | 45.6 | 50.2 and up |
| 30 to 40 | under 27.9 | 27.9 | 32.1 | 36.5 | 40.7 | 44.9 and up |
| 40 to 50 | under 24.6 | 24.6 | 28.2 | 32.0 | 35.8 | 39.5 and up |
| 50 to 60 | under 21.0 | 21.0 | 24.2 | 27.4 | 30.7 | 33.9 and up |
| 60 plus | under 17.6 | 17.6 | 20.3 | 23.0 | 25.7 | 28.4 and up |
Google also publishes a 13 to 20 row, omitted here. The tables come from published population norms and are not personal targets. Two points stand out. Bands are about five points wide, so a 10 percent estimation error can move you a whole level in either direction. And the decline with age is steep: a man who holds a VO2 max of 40 from 30 to 60 goes from Average to Very Good without getting any fitter, which is why Google suggests reading the number against your own three-month history rather than the label.
Accuracy: Fitbit versus the lab, Apple Watch and Garmin
Independent studies put Fitbit's run-based estimate in the same accuracy band as other wrist wearables. Two 2019 validations of the Fitbit Charge 2 against laboratory gas analysis, Klepin and colleagues in Medicine and Science in Sports and Exercise and Freeberg and colleagues in mHealth, reported mean absolute percentage errors of roughly 10 percent. A 2025 systematic review of wearable VO2 max accuracy in Frontiers in Sports and Active Living found the same pattern across brands: most devices land between 5 and 15 percent error, and all of them tend to over-estimate people with low fitness and under-estimate the very fit, because their models are trained on the middle of the population.
For comparison, a 2025 PLOS One study found Apple Watch under-estimated VO2 max by a mean of 6.1 ml/kg/min with a 13.3 percent error, and a 2024 study of the Series 7 reported 15.8 percent. Garmin's Firstbeat-based estimate has tested better in athletic groups: 7 to 8 percent for the Forerunner 245 in a 2025 European Journal of Applied Physiology paper and 6.9 percent for the Fenix 6 in a 2023 validation, though Garmin also under-reads highly trained runners by around 6 points. The honest summary is that no wearable, Fitbit included, is a substitute for a lab test when precision matters, but all are good enough to show direction over months. If you run seriously enough to care about the second decimal, the apps and watches built for that are compared in the best running apps of 2026 and is Whoop good for running.
Which devices support VO2 max, and is it Premium?
Any Fitbit or Pixel Watch that can pair heart rate with GPS produces the number. Built-in GPS: Charge 5 and Charge 6 ($159.95), Versa 3 and Versa 4 ($199.95), Sense and Sense 2 ($249.95) and every Pixel Watch, including the Pixel Watch 4 at $349.99 and Pixel Watch 5 from $399. Connected GPS from your phone: Inspire 2, Inspire 3 ($99.95) and Luxe, which means carrying the phone on the run. The screenless $99.99 Fitbit Air has no GPS and no connected GPS, so at publication its only route to a VO2 max is a run recorded by a third-party app and synced into Google Health, which Google says is now supported. Google's older help pages listed hardware back to the Alta HR and Charge 2 as compatible with the Cardio Fitness Score, but those devices are no longer sold. Prices and the full lineup are in the cheapest Fitbit in 2026.
VO2 max is free. In the Google Health app open the Fitness tab, scroll to Key metrics, tap See all if it is hidden, then tap VO2 max. You land on a three-month graph; the arrows cycle between quarters and the tabs above switch to monthly, quarterly or annual averages, with Learn more below the chart. Google Health Premium at $9.99 a month or $99.99 a year (£8.99 or £89.99 in the UK) adds a chat icon in the bottom corner of that screen for the Gemini-based Health Coach, which can explain the number and fold it into your weekly fitness plan. The metric itself has never been Premium-gated.
How to improve your Fitbit cardio fitness score
Two separate things move the number: getting fitter and giving the algorithm better data. On the data side, follow Google's own list. Run outdoors with GPS for at least 10 minutes, choose flat routes since only flat sections count, complete several runs rather than one, and run some of them at a faster pace, because higher-intensity efforts give a more accurate estimate. Wear the device to sleep so resting heart rate is measured properly, keep the band snug during runs, and give the GPS a minute to lock before you start. Runners who switch from running to spinning or the treadmill often see their score drift down simply because the app stops receiving qualifying runs.
On the fitness side, Google's advice matches the exercise-science consensus: raise the frequency and intensity of aerobic work, and use high-intensity intervals, which are especially effective at increasing VO2 max. A workable pattern for most people is three to four runs a week with one interval session (for example, four to six repeats of three minutes hard with three minutes easy), one longer easy run and the rest steady. Google says beginners can notice gains within weeks, experienced athletes take longer, and the number drops within a few weeks of stopping, so consistency matters more than any single workout. Judge progress over three months or more. Fitcoin, our own app, reads those runs from Apple Health or Health Connect and turns them into a daily FitScore, weekly Leagues and partner rewards, which is a reasonable way to keep the interval session on the calendar; if the idea of earning something for the miles appeals, apps that reward you for running compares the options.
Frequently asked questions
Is the Fitbit Cardio Fitness Score the same as VO2 max?
Yes. Cardio Fitness Score was Fitbit's consumer name for its VO2 max estimate, expressed in millilitres of oxygen per kilogram per minute and sorted into six levels from Poor to Excellent. When the Fitbit app became the Google Health app on May 19, 2026, Google renamed the metric VO2 max outright; the app's own label reads VO2 max, formerly known as cardio fitness score. The levels and the age and sex tables are unchanged.
Why does my Fitbit show a VO2 max range instead of a number?
In the old Fitbit app, users who never ran with GPS got a broad range estimated from resting heart rate, age, sex and weight, and a single number only after GPS runs. The Google Health app dropped the demographic estimate in May 2026, so a range no longer appears: you either have a GPS-based number or no VO2 max at all. To get one, track an outdoor run of at least 10 minutes with GPS; Google says it can take up to three runs within 30 days before the first value shows.
How accurate is Fitbit VO2 max?
Independent validation of Fitbit's run-based estimate against laboratory gas analysis has found mean absolute percentage errors of roughly 10 percent, in the same band as most wrist wearables. Studies of the Apple Watch report errors of about 13 to 16 percent with a tendency to underestimate fit runners, and Garmin Forerunner and Fenix models have scored 7 to 8 percent. A 10 percent error on a true VO2 max of 45 is 4 or 5 points, enough to move you a level, so use the three-month trend rather than one reading.
Does Fitbit VO2 max need Premium?
No. VO2 max sits in the Key metrics section of the Fitness tab in the free Base tier of the Google Health app, with the level, the age and sex tables and the three-month trend graph. Google Health Premium ($9.99 a month or $99.99 a year) adds a chat button on the VO2 max screen for the Gemini-based Health Coach and builds the number into your weekly fitness plan, but it does not unlock the metric.
Method: Checked September 8, 2026 using the Google Health help page on VO2 max, Google's May 2026 notes on the redesigned Google Health app, Google Store Fitbit and Pixel Watch listings, and peer-reviewed validation studies: Klepin et al. 2019 (Medicine and Science in Sports and Exercise), Freeberg et al. 2019 (mHealth), the 2025 Frontiers in Sports and Active Living systematic review, the 2025 PLOS One and 2024 JMIR Biomedical Engineering Apple Watch studies, and Garmin validations in the European Journal of Applied Physiology (2025) and Technologies (2023). Level tables are Google's published figures at publication. Prices are US list with UK prices where confirmed. Fitcoin has no commercial relationship with Google, Fitbit, Apple, Garmin, Whoop or any hardware brand named here. Wellness estimates only, not medical advice.
About the author: Harris Khan is the co-founder and CTO of Fitcoin, a UK fitness-rewards app.