Estimate your functional (fitness) age from physical performance
* Required — fitness norms differ by biological sex.
Educational / wellness tool. Not medical advice.
FitAge combines seven physical-performance tests plus one body-composition measure (waist-to-height). Each is calibrated against age in reference populations — five different cohorts with different age windows (US, Norway, Canada, Brazil, UK) — using the Klemera-Doubal framework; markers that change steeply with age and are low-noise carry more weight.
For more details on how to perform each test and the algorithm behind FitAge, see this walkthrough on Medium .
Maximum hand-grip force — a strong whole-body marker of muscle strength and healthy ageing.
Protocol: Best single-hand squeeze on a hand dynamometer — one hand, not both summed (highest of a few tries).
Modified push-up repetitions in 40 seconds — upper-body strength-endurance.
Protocol: On your toes with a straight body: from lying face-down (hands by your shoulders), push up to full arm extension, tap one hand on top of the other at the top, then lower your whole body back to the floor. Count full reps in 40 seconds.
Time to stand and sit five times from a chair — lower-body power. Faster (fewer seconds) is better.
Protocol: Arms across chest, 5 full sit-to-stands as fast as safely possible, timed.
Sitting down to and rising from the floor using as little support as possible (0-10). Higher is better.
Protocol: Start at 10; subtract 1 per hand/knee support used, 0.5 per wobble, for sitting and rising.
Summed one-leg standing time (OLSsum): eyes open PLUS eyes closed. Note: the source authors themselves question whether OLSsum is a fully valid measure of balance.
Protocol: Stand on your best leg, hands on hips — time it with eyes open, then with eyes closed, each capped at 60 s. Enter the two times added together (max 120 s).
Forward reach past the toes — hamstring and lower-back flexibility.
Protocol: Seated, straight back, reach forward; cm past (+) or short of (-) the toes.
Waist circumference divided by height — central adiposity. Lower is generally healthier (aim < 0.5).
Protocol: Waist measured at the top of the hip bone (iliac crest), at the end of a normal breath; waist and height in the same units, entered below.
Visual reaction time on a card-matching task — processing speed. Faster (lower ms) is better. As a proxy you can use a general reaction-time app, like lights out.
Protocol: Mean time to respond as soon as two on-screen cards match (a "Snap" matching task), in milliseconds.
Functional age estimates how well your body performs physically compared with others your chronological age. It is built from fitness tests — strength, balance, flexibility, body composition, and reaction time — rather than blood markers.
FitAge adapts the Klemera-Doubal Method (KDM) framework to these functional markers. Each marker is calibrated against age in reference populations (a patchwork of five cohorts with different age windows), and the markers are combined into a single estimate, regularized toward your chronological age.
Exploratory and educational. Fitness markers are individually weaker age predictors than blood biomarkers, and FitAge has not been validated against health outcomes — it is not a clinical biological-age clock. Reference data are assembled from several population cohorts.
Functional < Chronological
Fitter than typical
Functional ≈ Chronological
Typical for your age
Functional > Chronological
Room to improve
How to measure your biological age for free
— walkthrough of the tests and the algorithm behind FitAge.
FitAge source code on GitHub
— open-source code and coefficients.
Klemera & Doubal (2006), Mech Ageing Dev — the KDM framework adapted here.
Coefficients assembled from NHANES, Kjær 2016 (Norway), Mayhew 2023 (CLSA), Araújo 2020 (SRT), and UK Biobank (Talboom 2021).