Fitness Age Calculator: How Fit Are You for Your Age?

Fitness age answers a simple question: is your heart and lung fitness typical for your age, or closer to that of someone younger or older? Researchers in the Cardiac Exercise Research Group at the Norwegian University of Science and Technology (NTNU) built the idea on the HUNT Fitness Study, in which several thousand healthy adults in central Norway had their VO2 max measured on a treadmill in 2007 and 2008. Their online fitness calculator estimates fitness from age, waist or body mass index, leisure-time exercise and resting heart rate (NTNU CERG).

This free fitness age calculator follows the same two steps with published numbers you can check. It estimates your VO2 max with the HUNT equation for your sex (Nes et al. 2011), then finds the age at which healthy Norwegian adults of your sex averaged that VO2 max (Loe et al. 2013). The equation comes from one paper and the averages from another, and both come from the same HUNT 3 Fitness Study. We could not find the exact conversion that NTNU's own calculator uses in a paper we could read, so your result here can differ from theirs.

What fitness age means

Your fitness age is the age at which your VO2 max would be exactly average for your sex. VO2 max, also called peak oxygen uptake, is measured in milliliters of oxygen per kilogram of body weight per minute (mL/kg/min), and it falls with age. In the HUNT Fitness Study, healthy women averaged 43.0 mL/kg/min in their 20s and 28.3 at 70 and over, and men averaged 54.4 and 35.3. Find where your number sits on that slope and you have your fitness age.

So a 50-year-old man with a VO2 max of 48 mL/kg/min has a fitness age of 41, because, reading between the decade averages, that is the HUNT average for men aged 41. A 35-year-old woman at 34 mL/kg/min has a fitness age of 56. A fitness age below your real age means you are fitter than average for your age and sex; one above it means you are less fit. The number describes aerobic fitness only. It says nothing about strength, flexibility, blood pressure or any disease.

How this fitness age calculator works

Step 1: estimate VO2 max with the HUNT equation

Nes and colleagues measured VO2 max directly in 4,637 healthy adults and used regression to find which simple measures predicted it best. Age, waist circumference, leisure-time exercise and resting heart rate, in that order, were the strongest predictors for both sexes. The final equations, built on 2,067 men and 2,193 women with an average age of about 48, are:

Women: VO2 max = 74.736 − 0.247 × age − 0.259 × waist (cm) − 0.114 × resting heart rate + 0.198 × exercise scoreMen: VO2 max = 100.27 − 0.296 × age − 0.369 × waist (cm) − 0.155 × resting heart rate + 0.226 × exercise score

The 2011 paper is behind a paywall, so we read these coefficients where other researchers reprint them in open-access papers: Table 1 of a US validation study by Peterman and colleagues (2020), the formula supplement of a HUNT study on rheumatoid arthritis (Liff et al. 2021) and a 2026 HUNT paper with Nes as a coauthor (Førland Havstad et al. 2026). All three print the same coefficients, with the women’s intercept given as 74.736 by Peterman and rounded to 74.74 in the HUNT papers, and the fit they report matches the original abstract: the equations explain 61 percent of the variation in measured VO2 max in men and 56 percent in women, with a standard error of 5.70 and 5.14 mL/kg/min.

Take the default example. A 40-year-old woman with a 32-inch (81.3 cm)an 81.3 cm waist, a resting heart rate of 68 and an exercise score of 15 gets 74.736 − 9.88 − 21.05 − 7.75 + 2.97, which is 39.0 mL/kg/min.

The exercise score

The exercise score comes from three HUNT questionnaire answers multiplied together. The points below are from Table 1 of Liff and colleagues (2020), who reprint the scoring developed for the original HUNT equation:

Easy sessions score zero however often you do them, so the score rewards exercise that makes you breathe hard and sweat. The highest possible score is 3 × 10 × 1.5 = 45. The HUNT questionnaire split session length into four answers, but under 15 minutes and 16 to 30 minutes both score 1, and 30 to 60 minutes and over an hour both score 1.5, so the calculator asks only the two that matter.

Step 2: find the age at which that VO2 max is average

Loe and colleagues published the average treadmill VO2 max of 3,816 healthy HUNT participants aged 20 to 90, by sex and decade. People with heart disease, lung disease, cancer or blood pressure medicine were left out. These are the averages from their Table 2, in mL/kg/min:

The calculator places each decade's average at the middle of the decade (ages 25, 35, 45, 55 and 65) and draws straight lines between them. The paper gives one average for everyone 70 and over without their average age, so the calculator places that one at 75; this is our convention, not a published number. Your fitness age is the point on the line for your sex where the average equals your VO2 max. Above the average for the 20s the calculator shows "under 25", and below the average for 70 and over it shows "over 75", rather than stretching the lines past the data.

The default woman's 39.0 mL/kg/min sits between the averages for the 30s (40.0) and the 40s (38.4), a little past the middle of that stretch, which puts her fitness age at 41. Because both steps come from HUNT, an adult whose waist, pulse and exercise are typical for HUNT participants of their age lands close to their real age.

Fitness age vs metabolic age vs biological age

The three names sound alike but measure different things.

• Fitness age, the one on this page, comes from VO2 max. The equation and the averages behind it are published, so anyone can check the arithmetic.
• Metabolic age is a number many body composition scales print. The scale maker Tanita says it compares your estimated basal metabolic rate with the average for your age group (Tanita), but its help page gives no formula or averages, so the number cannot be checked or compared between brands.
• Biological age usually means a lab estimate of how fast your body is aging. Well-studied versions read chemical marks on DNA from a blood sample, such as DNAm PhenoAge (Levine et al. 2018). They need a lab test, so an online quiz that promises your biological age is not measuring the same thing.

Of the three, fitness age is the one you can test at home, change with training and recheck in a few minutes.

What VO2 max predicts for your health

Fitness age matters because VO2 max is one of the strongest single predictors of how long people live. Researchers often count fitness in METs, where 1 MET is 3.5 mL/kg/min. In a meta-analysis of 33 studies and 102,980 healthy adults, each 1-MET higher fitness level went with a 13 percent lower risk of death from any cause and a 15 percent lower risk of heart disease and other cardiovascular events (Kodama et al. 2009). Among 122,007 adults who took a treadmill test at the Cleveland Clinic, people in the bottom 25 percent for fitness had about 5 times the risk of death of the elite top 2.3 percent after other risk factors were taken into account (Mandsager et al. 2018).

Estimated fitness predicts too. When the NTNU group applied its non-exercise model to about 37,000 adults from the first HUNT survey (1984 to 1986) and followed them for an average of 24 years, a higher estimate went with lower risk of death in people under 60. Each 1 MET higher went with a 21 percent lower risk of dying of cardiovascular disease, in men and in women (Nes et al. 2014). In a later HUNT analysis of 38,480 adults followed for a median of 16 years, low estimated fitness predicted death from cardiovascular disease, and adding traditional clinical risk factors barely improved the prediction (Nauman et al. 2017).

A 2016 American Heart Association scientific statement makes the case for treating fitness as a clinical vital sign (Ross et al. 2016), and Peterman's team reads it as recommending at least a non-exercise estimate like this one at routine checkups. These studies show associations, not proof that raising your number adds a set amount of life. Our article on VO2 max and longevity walks through the evidence.

How to lower your fitness age

Your fitness age drops when your VO2 max rises, and VO2 max responds to training. A meta-analysis of 28 controlled trials in healthy adults aged 18 to 45 found that steady endurance training raised VO2 max by 4.9 mL/kg/min more than no exercise did, and high-intensity interval training by 5.5, with intervals ahead of steady training by about 1.2 (Milanović et al. 2015). The volunteers were in their mid-20s on average, so read the size of the gains as a guide rather than a promise.

In fitness age terms, 5 mL/kg/min is a big change. For the default woman at 39.0, it would mean 44.0, above the HUNT average for women in their 20s, and a fitness age under 25.

A simple plan for a beginner is two or three sessions a week of 30 minutes or more that leave you breathing hard and sweating, with one of them turned into intervals once you have a few weeks of steady work behind you. Brisk walking counts if it gets you there. Our guide to an interval running workout gives sessions to start with, the heart rate zone calculator sets the intensity for each one, and our review of HIIT vs steady-state cardio compares the two approaches in more detail.

The equation also shows which answers move your estimate. For the default woman, pushing close to exhaustion instead of just sweating lifts her exercise score from 15 to 30 and her estimate by 3.0, for a fitness age of 28. Exercising almost every day instead of 2 to 3 times a week gives 33, a waist 2 inches5 cm smaller gives 34, and a resting pulse 5 beats lower gives 38. The result card lists these changes for your own inputs. They show how the equation responds, not a promise of what training will do: in a US study, changes in this estimate tracked real changes in VO2 max only moderately, as the next section explains.

How accurate is a fitness age calculator?

It is less accurate than one neat number suggests. The HUNT equation's standard error of estimate is 5.70 mL/kg/min for men and 5.14 for women, so roughly two in three people's measured VO2 max falls within that distance of their estimate, and the rest fall further away.

Why the error is large in years

Converted to years, that error is large, because the HUNT averages change slowly across midlife. Between the 30s and 40s, the women's average fell only from 40.0 to 38.4 and the men's from 49.1 to 47.2. In that stretch, each 1 mL/kg/min moves a woman's fitness age by about 6 years and a man's by about 5. For a 40-year-old woman whose estimate matches the average for her age, one standard error either way spans fitness ages from under 25 to 56. For a 40-year-old man it spans 26 to 55. The result card shows this likely range for your own inputs, and it only calls your fitness age younger or older than your real age when your real age falls outside it.

How the equation did in US adults

Peterman and colleagues tested 27 non-exercise equations against treadmill tests in 987 adults at Ball State University in Indiana. For the HUNT equation, in the 676 people with the needed measurements, the estimate followed measured VO2 max fairly well (R² 0.67, standard error 4.4 mL/kg/min) but read high: the estimates averaged 40.9 mL/kg/min, significantly different from the treadmill results, which averaged 34.9 across the whole group. One likely reason is that HUNT volunteers were unusually fit. Loe's team found their VO2 max about 20 percent higher than North American reference data after adjusting for body size. Because the equation and the averages both come from HUNT, the two effects partly cancel in the fitness age, but the VO2 max number on the card may run several points above what a US lab would measure. The Ball State team also had to convert their own activity questions to the HUNT scoring, which may have added some error.

Tracking change over time

Change is harder to catch than a single level. In the same US group, changes in the HUNT estimate between two tests agreed with changes in measured VO2 max better than those of any of the other 26 equations (intraclass correlation 0.63). It still put the average gain at 1.0 mL/kg/min when the treadmill showed 1.8, and it flagged 65 percent of real improvements and 61 percent of real declines. In a second Ball State analysis of 28 equations and 2,529 treadmill tests, only 52 percent of people were placed in the right one of three fitness categories (Peterman et al. 2021). In 93 adults with rheumatoid arthritis, the HUNT equation overestimated fitness (R² 0.48, error 7.07 mL/kg/min), which led Liff's team to build a separate equation for that group.

For a more exact fitness age, measure instead of estimate. A field test such as the 12-minute Cooper test or the 1-mile walk in our VO2 max calculator measures your fitness directly instead of predicting it from your waist and habits, and that page lists each test's typical error. A lab test with a breathing mask is closest of all: in the HUNT lab, two treadmill tests on the same person usually agreed within about 2 mL/kg/min. Then look up your result in the table below.

Worked examples: eight people through the calculator

Each row runs the calculator once. Exercise is how often, how hard and how long, with the exercise score in brackets. The likely range is one standard error either way, and the band compares it with real age.

Three patterns stand out. The 55-year-old woman walks almost every day, but at an easy pace her exercise score is zero, so her estimate rests on age, waist and pulse alone. The 60-year-old man's fitness age is 10 years below his real age, yet the band still says about your age, because one standard error spans 32 to 65 for him. And the two 45-year-olds who exercise less than once a week land about 20 years older than their real age.

Fitness age by VO2 max

If you already have a VO2 max from a lab test, a watch or a field test, read your fitness age here. These are the conversions the calculator uses, from the HUNT averages above. HUNT measured VO2 max on a treadmill, and Peterman's team notes that a cycling test often gives a different value.

When to ignore this calculator

The HUNT equation and averages come from healthy adults. In these situations the number can mislead you, and a clinician is the better guide.

• Heart or lung disease, or symptoms during exercise. Chest pain, unusual breathlessness, dizziness or palpitations are reasons to see a doctor. A clinical exercise test is the right tool.
• Medicines that change heart rate. Beta blockers and some other drugs lower your resting pulse, which the equation reads as fitness, so your fitness age comes out younger than it should. Ask your prescriber before relying on it.
• Pregnancy. Waist size and resting heart rate both change during pregnancy, so neither input means what the equation expects. Talk to your obstetric care team about exercise.
• Rheumatoid arthritis. The HUNT equation overestimated fitness in adults with rheumatoid arthritis, and Liff's team published a separate equation for them.
• Teenagers. HUNT tested adults aged 20 to 90. Young people need youth fitness standards.
• Illness or fever. Wait until you feel well before you take your resting pulse, so the reading reflects your normal day.
• An eating disorder, now or in the past. Focusing on waist size can be harmful. Work with your treatment team.

Related reading

References

1. Nes BM, Janszky I, Vatten LJ, Nilsen TI, Aspenes ST, Wisløff U. "Estimating VO2peak from a nonexercise prediction model: the HUNT Study, Norway." Med Sci Sports Exerc. 2011;43(11):2024-2030. doi:10.1249/MSS.0b013e31821d3f6f, PubMed 21502897. Only the abstract is open; the coefficients were read in references 2 to 4.
2. Peterman JE, Harber MP, Imboden MT, Whaley MH, Fleenor BS, Myers J, Arena R, Finch WH, Kaminsky LA. "Accuracy of nonexercise prediction equations for assessing longitudinal changes to cardiorespiratory fitness in apparently healthy adults: BALL ST cohort." J Am Heart Assoc. 2020;9(11):e015117. doi:10.1161/JAHA.119.015117, PMC7428991. Table 1 prints the HUNT equations; Tables 5, 6 and 8 give the US results.
3. Liff MH, Hoff M, Wisløff U, Videm V. "Reduced cardiorespiratory fitness is a mediator of excess all-cause mortality in rheumatoid arthritis: the Trøndelag Health Study." RMD Open. 2021;7(1):e001545. doi:10.1136/rmdopen-2020-001545, PMC7942264. Online supplemental data 1 prints the HUNT equations.
4. Førland Havstad L, Woodhouse A, Landmark T, Stensvold D, Nes B, Skagseth M, Glette M. "Cardiorespiratory fitness and pain severity: longitudinal associations from the general population. The HUNT study." Pain Rep. 2026;11(3):e1447. doi:10.1097/PR9.0000000000001447, PMC13132283
5. Liff MH, Hoff M, Fremo T, Wisløff U, Videm V. "An estimation model for cardiorespiratory fitness in adults with rheumatoid arthritis." Med Sci Sports Exerc. 2020;52(6):1248-1255. doi:10.1249/MSS.0000000000002250, PubMed 31977641. Table 1 gives the HUNT exercise score.
6. Loe H, Rognmo Ø, Saltin B, Wisløff U. "Aerobic capacity reference data in 3816 healthy men and women 20-90 years." PLoS One. 2013;8(5):e64319. doi:10.1371/journal.pone.0064319, PMC3654926. A 2013 correction fixed the layout of Table 2 in the PDF; the values used here match the corrected table.
7. Cardiac Exercise Research Group, NTNU. "Fitness calculator." ntnu.edu/cerg/vo2max, read November 7, 2026.
8. Nes BM, Vatten LJ, Nauman J, Janszky I, Wisløff U. "A simple nonexercise model of cardiorespiratory fitness predicts long-term mortality." Med Sci Sports Exerc. 2014;46(6):1159-1165. doi:10.1249/MSS.0000000000000219, PubMed 24576863. A corrigendum appeared in Med Sci Sports Exerc. 2020;52(6):1440; we could not read its text.
9. Nauman J, Nes BM, Lavie CJ, Jackson AS, Sui X, Coombes JS, Blair SN, Wisløff U. "Prediction of cardiovascular mortality by estimated cardiorespiratory fitness independent of traditional risk factors: the HUNT Study." Mayo Clin Proc. 2017;92(2):218-227. doi:10.1016/j.mayocp.2016.10.007, PubMed 27866655
10. Kodama S, Saito K, Tanaka S, et al. "Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis." JAMA. 2009;301(19):2024-2035. doi:10.1001/jama.2009.681, PubMed 19454641
11. Mandsager K, Harb S, Cremer P, Phelan D, Nissen SE, Jaber W. "Association of cardiorespiratory fitness with long-term mortality among adults undergoing exercise treadmill testing." JAMA Netw Open. 2018;1(6):e183605. doi:10.1001/jamanetworkopen.2018.3605, PMC6324439
12. Ross R, Blair SN, Arena R, et al. "Importance of assessing cardiorespiratory fitness in clinical practice: a case for fitness as a clinical vital sign: a scientific statement from the American Heart Association." Circulation. 2016;134(24):e653-e699. doi:10.1161/CIR.0000000000000461, PubMed 27881567
13. Peterman JE, Whaley MH, Harber MP, Fleenor BS, Imboden MT, Myers J, Arena R, Kaminsky LA. "Comparison of non-exercise cardiorespiratory fitness prediction equations in apparently healthy adults." Eur J Prev Cardiol. 2021;28(2):142-148. doi:10.1177/2047487319881242, PubMed 33838037
14. Milanović Z, Sporiš G, Weston M. "Effectiveness of high-intensity interval training (HIT) and continuous endurance training for VO2max improvements: a systematic review and meta-analysis of controlled trials." Sports Med. 2015;45(10):1469-1481. doi:10.1007/s40279-015-0365-0, PubMed 26243014
15. Levine ME, Lu AT, Quach A, et al. "An epigenetic biomarker of aging for lifespan and healthspan." Aging (Albany NY). 2018;10(4):573-591. doi:10.18632/aging.101414, PubMed 29676998
16. Tanita Europe. "What is metabolic age?" support.tanita.eu, read November 7, 2026.

How this calculator differs from typical fitness age calculators

Most online fitness age calculators give one confident number and say little about how they reached it. Some turn VO2 max into an age with a formula that names no source, and some mix fitness age up with the metabolic age that bathroom scales print. Few mention that a non-exercise estimate is typically off by about 5 mL/kg/min, or that in midlife a single point of VO2 max can move a fitness age by five years or more.

This calculator uses the published HUNT equation for your sex, the exercise scoring developed for it and the treadmill averages of 3,816 healthy adults from the same study, and the page names where each number was read. It shows the likely range around your result, calls your fitness age younger or older only when your real age falls outside that range, and reports how the equation did when US researchers tested it. Every input is checked against realistic adult ranges, and an estimate outside the VO2 max values HUNT measured is flagged instead of converted.