people usually think that BMI (body mass index) is the best way to do so but it’s not tru. Think of it- we can be the same height and weight but I’ll be a couch potato and you a body builder. I’m an athlete, (bicycle racer) and I go to regular checkups at a sport clinic. They check what they call VO2max. that means – the oxygen volume that you consume. Unfortunately you can’t do this at home, but doctors recommend a yearly checkup here is a short video that explains it and say how to check it up and how to improve it: