Healthy body calculator from Ask the Dietitian . Symptom checker from OnHealth . Basal Metabolism Calculator from Room 42 Software . There's nothing that can't be boiled down to a number.
Many calculators are similar.
You plug in your height, weight, and date of birth, then answer questions about your health and family history. Sites score you against other registered users. It's hard to know just what the resulting number means, but you can see what would happen to your score if your habits were healthier. When I agreed to cut back on fatty foods, for example, WellMed upped my score by two points, from 169 to 171. The extensive questioning you'll get at some sites makes these verdicts seem even more precise.