A fitness calculator is a useful measurement of your fitness to play tennis or any other activity for that matter. It is a rough guide in determining whether your body can stand the rigors of physical activity which tennis demands. Before you start to play any sports, be sure to consult your physician if you are unsure of your physical condition due to age or inactivity.
This website has calculators for your needs as a tennis player and for other aspects of your overall health. Feel free to use them, even add them to your website (if you have one).
This line of health calculators let you calculate your target heart rate, determine your nutritional needs among other useful health checks.
If you want any fitness calculator for your website, go here: