This calculator uses a series of metrics to determine your fitness age, so you can compare it against your actual age.
The model used for this prediction was validated on over 500,000 participants in a 2024 study and was demonstrated to be 93.6% accurate for adults between the ages of 20 and 64.
For a full synopsis of the original study, as well as a breakdown of their predictive equation, head here. Or you can read the study here.
You will need the following information to complete the calculator. Click on each metric to get more information and instructions.
VO₂ max is calculated by most wearables. Or there are several ways to calculate it manually, which are explained here.
To measure grip strength, you'll need to purchase a simple machine like this one. View on Amazon
To perform a proper sit-up, lie on your back with your knees bent and feet flat on the floor, hip-width apart. Cross your arms over your chest or place your hands lightly behind your head without pulling on your neck. Engage your core and use your abdominal muscles to lift your upper body toward your knees, keeping your lower back in contact with the floor as long as possible. Exhale as you rise, then slowly lower yourself back down with control while inhaling. Repeat for the desired number of repetitions.
In the Sit & Reach test, the distance is measured relative to the toes as the baseline (zero point). Sitting with legs fully extended and feet flat against a measurement box or ruler, the participant reaches forward as far as possible.
This measurement provides a clear indication of hamstring and lower back flexibility, with higher positive scores reflecting greater flexibility.
Your current body weight is required to compute relative grip strength. Please ensure you have an up-to-date measurement.
Enter the below information to calculate your fitness age.
Disclaimer: This is purely a prediction based on the 500,000 participants from the original study. Read more here.
The study used multiple linear regression to determine how much each metric influenced the predicted fitness age. The relative importance of each metric can be determined by looking at the regression coefficient (β value)—the larger the absolute value, the stronger the influence on the fitness age prediction.
Below is the ranking from most to least important, based on the regression equation for adults (ages 20–64):
| Rank | Metric | Regression Coefficient | Influence |
|---|---|---|---|
| 1 | Relative Grip Strength | -1.171 | Strongest predictor—higher grip strength reduces fitness age significantly |
| 2 | VO₂ max | -0.029 | Moderate predictor—higher endurance lowers fitness age |
| 3 | Sit-ups (Muscular Endurance) | -0.032 | Small negative effect—more sit-ups slightly lower fitness age |
| 4 | Sit-and-Reach (Flexibility) | +0.032 | Small positive effect—more flexibility slightly increases fitness age |
| 5 | Sex (Male = 1, Female = 2) | +0.769 | Females tend to have a higher fitness age compared to males |
If you're keen to track your own fitness age, this is the formula used by the original study to predict fitness age:
Fitness age for adults = 100.882 – (0.029 × VO₂max) – (1.171 × Relative Grip Strength) – (0.032 × Sit-up) + (0.032 × Sit and reach) + (0.769 × (Sex: male = 1; female = 2))
Head back to cerebraldefence.com to explore research and tactics for improving your physical fitness and neurological health.
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