FitAge
Estimate your functional (fitness) age from physical performance
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Age
Biological Sex *
Select...<br>Female<br>Male
* Required — fitness norms differ by biological sex.
Strength & Power
Grip strength (kg)
Push-ups (reps / 40 s)
Chair rise 5x (sec)
Floor sit-rise (0-10)
Balance & Flexibility
One-leg balance (sec)
Sit-and-reach (cm)
Body & Reaction
Waist (cm)
Height (cm)
Reaction time (ms)
Calculate<br>Educational / wellness tool. Not medical advice.
Understanding Your Markers
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<br>this walkthrough on Medium
Grip strength
Maximum hand-grip force — a strong whole-body marker of muscle strength and healthy ageing.
Protocol:<br>Best single-hand squeeze on a hand dynamometer — one hand, not both summed (highest of a few tries).
Tips
Train grip directly: dead hangs, farmer carries, heavy holds
Do regular resistance training for the whole body
Ensure adequate protein intake
Push-ups (modified)
Modified push-up repetitions in 40 seconds — upper-body strength-endurance.
Protocol:<br>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.
Tips
Practice push-ups 2-3x/week, progressing reps
Build pressing strength (incline press, dips)
Strengthen the core and shoulders
Chair rise (5x)
Time to stand and sit five times from a chair — lower-body power. Faster (fewer seconds) is better.
Protocol:<br>Arms across chest, 5 full sit-to-stands as fast as safely possible, timed.
Tips
Train squats and sit-to-stands
Add step-ups and lunges for leg power
Practice rising without using your hands
Floor sit-and-rise
Sitting down to and rising from the floor using as little support as possible (0-10). Higher is better.
Protocol:<br>Start at 10; subtract 1 per hand/knee support used, 0.5 per wobble, for sitting and rising.
Tips
Practice getting up and down from the floor daily
Improve hip/ankle mobility and single-leg strength
Work on balance and core control
One-leg balance
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:<br>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).
Tips
Practice single-leg stands daily (eyes open, then closed)
Add balance work: tandem stance, wobble drills
Strengthen ankles, hips, and core
Sit-and-reach
Forward reach past the toes — hamstring and lower-back flexibility.
Protocol:<br>Seated, straight back, reach forward; cm past (+) or short of (-) the toes.
Tips
Stretch hamstrings and hips regularly
Add mobility/yoga sessions
Warm up before stretching for best range
Waist-to-height ratio
Waist circumference divided by height — central adiposity. Lower is generally healthier (aim
Protocol:<br>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.
Tips
Reduce central fat through diet quality and activity
Combine cardio with strength training
Prioritise sleep and stress management
Reaction time
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:<br>Mean time to respond as soon as two on-screen cards match (a "Snap" matching task), in milliseconds.
Tips
Train with reaction drills and ball sports
Prioritise sleep and limit alcohol
Stay physically active to support brain processing speed
What is Functional Age?
Functional age estimates how well your body performs physically compared with others your chronological age.<br>It is built from fitness tests — strength, balance, flexibility, body composition, and reaction time — rather than blood markers.
FitAge<br>adapts the Klemera-Doubal Method (KDM) framework<br>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...