Fitness Age on Apple Watch: Find and Track Yours

Apple Watch records the Cardio Fitness input that Body Insights uses for Fitness Age. Body Insights reads the available value in the background and converts it into your Fitness Age for free. Use the browser calculator for an immediate result. You can also open your first full Fitness Age view free in the iPhone app.

You need your current age and latest Cardio Fitness value. You also need the female or male reference curve that matches your Body Insights profile. The result is a whole-year Fitness Age plus the difference from your actual age.

Body Insights

See your first Fitness Age free.

Body Insights reads your selected VO2 max, age, and reference curve, then shows the matching age and the gap from your actual age.

See my Fitness Age free

Find your VO2 max and Fitness Age in Body Insights

Body Insights shows the result and the input in one place.

Open Body Insights.
On the Body tab, open Fitness Age.
Read your Fitness Age and the difference from your actual age.
Scroll to Contributing Factors to see the VO₂ Max value in ml/kg/min.
Review Fitness Age Trend to compare recent months.

Apple Watch Series 3 or later estimates Cardio Fitness during Outdoor Walk, Outdoor Run, and Hiking workouts. Apple supports values from 14 to 65 ml/kg/min. Indoor workouts do not create this estimate.

If Body Insights has no Fitness Age yet, Apple says the first Cardio Fitness estimate can require at least 24 hours of watch wear. It can also need several supported outdoor workouts and passive measurements. Check your age and biological sex in Body Insights User Information. Apple's Cardio Fitness instructions list the watch requirements.

Calculate your Fitness Age free

Open the free Fitness Age calculator, enter the three fields below, and tap Calculate my fitness age. The calculator gives you the result in whole years.

Field	Enter	What it controls
Current age	A whole number from 18 to 100	The younger or older comparison and the app's extreme-result bound.
Reference curve	Female or male	The VO2 max reference line used for the age match. Use the biological sex in your Body Insights profile.
Apple Watch VO2 max	A value from 14.0 to 65.0 ml/kg/min	The point Body Insights converts into a matching aerobic age.

The calculator returns the matching Fitness Age in whole years. It then subtracts that result from your current age to show the gap.

Years younger = current age - Fitness Age

If that number is negative, reverse the subtraction and read the result as years older.

Use the Fitness Age formulas

Body Insights maps VO2 max onto a straight reference line from age 18 to age 65. The female curve runs from 54 to 22 ml/kg/min. The male curve runs from 58 to 26 ml/kg/min. Both curves fall by 32 points across 47 years.

Use the formula for the reference curve in your Apple Health profile:

Female Fitness Age = floor(18 + 47 × (54 - VO2 max) / 32)

Male Fitness Age = floor(18 + 47 × (58 - VO2 max) / 32)

floor means round down to the previous whole year. If the raw result is below 18, the calculator reports 18.

The iPhone app also keeps extreme results within 20 years of your current age. It then limits the final Fitness Age to 18 through 99.

Age-bounded result = clamp(raw Fitness Age, current age - 20, current age + 20)

App Fitness Age = floor(clamp(age-bounded result, 18, 99))

This bound stops one unusual VO2 max sample from producing an age gap far outside the reference data. Most ordinary results do not touch the bound.

These reference anchors follow the HUNT 3 Fitness Study. Researchers directly measured peak oxygen uptake in 4,631 healthy adults across a wide adult age range.

Follow two worked examples

These examples use the same formulas as the free calculator.

Example	Calculation	Fitness Age	Compared with actual age
Female curve, age 45, VO2 max 30.0	18 + 47 × (54 - 30) / 32 = 53.25	53	53 - 45 = 8 years older
Male curve, age 45, VO2 max 46.0	18 + 47 × (58 - 46) / 32 = 35.63	35	45 - 35 = 10 years younger

The first example does not mean the person's whole body is 53. It means a VO2 max of 30.0 sits near the age-53 point on the female aerobic-fitness reference curve.

Notice that current age does not move the raw curve match. It tells you how many years younger or older that match is. In the app, current age also sets the 20-year safety bound for an extreme result.

See your first Fitness Age free in Body Insights

Body Insights is a free iPhone app that reads your selected Cardio Fitness value from Apple Health and does the calculation for you. Open the Body tab and tap the Fitness Age card. Your first full Fitness Age view is free.

Fitness Age 30, 10 years younger — Tap the Fitness Age card to open the full view.

The screen shows:

Your Fitness Age in whole years
The signed difference from your actual age
Whether the result is younger, older, or the same
The VO2 max value and female or male reference input
A six-month Fitness Age history
Your Improvement percentage and age-group ranking

The free browser calculator remains available when you want to run another manual check. Body Insights reads the selected VO2 max, age, and biological sex. It removes the copying and arithmetic, then keeps the result beside your six-month history.

Body Insights can also calculate an optional VO2 max estimate from your highest and resting heart rates. The Calculated VO2MAX card labels this source and lets you choose Use as Default.

Fitness overview with calculated VO2 max 53.4 — The screen keeps the calculated value beside your weekly fitness data.

Calculated VO2 max = 15.3 × highest heart rate / resting heart rate

That heart-rate-ratio estimate is a different source from Apple Health Cardio Fitness. Check the source label before you compare results from two dates.

Read the six-month trend

One Fitness Age is a snapshot. Body Insights converts each usable monthly VO2 max point with the same reference curve and plots up to six completed months. Lower is the favorable direction.

Fitness Age trend moving from an older starting point toward a younger result across six months — A six-month Fitness Age trend. Lower is the favorable direction.

The Improvement percentage compares the first usable month with the latest usable month:

Improvement % = (first Fitness Age - latest Fitness Age) / first Fitness Age × 100

If Fitness Age falls from 50 to 45, the calculation is (50 - 45) / 50 × 100 = 10%. Body Insights shows +10% Improvement. If Fitness Age rises, the percentage becomes negative.

A new supported workout or a correction to your Apple Health profile can move the next Cardio Fitness estimate. Compare several readings across weeks or months. If your energy varies, use a pace you can sustain instead of chasing a younger number with one hard workout.

Fix a missing or surprising result

Check the source before changing anything. A missing Cardio Fitness value and an unexpected Fitness Age have different fixes.

Confirm that Contributing Factors in Body Insights shows a VO₂ Max value between 14 and 65 ml/kg/min.
Check the age and biological sex saved in your Body Insights profile.
Check whether Body Insights says From Apple Health or Calculated from heart rate.
Use the same source when you compare two results.
Rerun the free calculator with the exact value shown to one decimal place.

The Apple Watch estimate is not the same as a laboratory VO2 max test. Its best use is following the direction across repeated estimates made under similar conditions.

Related Fitness Age guides

Body Insights

See the number without doing the math.

Your first full Fitness Age view is free in Body Insights. See the age, the gap from your actual age, and the six-month trend.

See my Fitness Age free