Health calculators are screening and planning tools, not diagnoses. A BMI flags who should look closer; it cannot see muscle, bone or where fat is carried. A calorie target is a starting hypothesis to test against your own weight trend over two or three weeks. A due date is the middle of a five-week normal window, not an appointment. Used that way — as well-made estimates that start better conversations with professionals — these tools are genuinely valuable.
Each calculator on BeadCalc states its method on the page: the Mifflin-St Jeor equation for calories, the US Navy circumference method for body fat, Naegele's rule for due dates, the Devine and companion formulas for ideal weight. Where a method has known error bars, the page says so. If you are pregnant, managing a condition, or making decisions about medication or treatment, your clinician's numbers always outrank a website's.