The Fitness Age Calculator estimates how fit your body is compared to your actual age by analyzing your resting heart rate (RHR), VO₂ Max, and chronological age. It uses the formula Fitness Age = Actual Age + (RHR − 60)/2 − (VO₂ Max − 35)/2 to estimate your body’s biological or performance-based age. A lower resting heart rate and a higher VO₂ Max generally indicate a younger fitness age, reflecting better cardiovascular efficiency and endurance. This calculator helps users assess overall fitness, track progress through regular exercise, and understand how lifestyle and training impact heart health and physical vitality over time.