Health Calculators

Health calculators handle the math that comes up in everyday wellness, nutrition, and health-related financial planning. Our coverage spans body composition (BMI, body fat, lean body mass, ideal weight), nutrition (calories, protein, keto macros), reproductive health (due date, ovulation, pregnancy timeline), and the financial side (HSA contributions, A1C interpretation).

The BMI calculator uses the standard CDC formula (kg/m² or 703 × lb/in²) and reports the WHO weight categories. BMI is a useful screening tool but a poor measure of health in muscular individuals — for those cases the body fat percentage calculator (using the U.S. Navy method) is a better proxy. The basal metabolic rate (BMR) and calorie calculators use Mifflin-St Jeor equations, which are the current standard for most clinical and fitness applications (replacing the older Harris-Benedict equations that overestimate by ~5% for most adults).

The pregnancy and ovulation tools use Naegele's rule (LMP + 280 days) for due dates and standard cycle-tracking math for ovulation windows. These are estimates and should never substitute for OB/GYN-confirmed ultrasound dating.

The A1C calculator converts hemoglobin A1C percentage to average blood glucose using the ADAG (A1C-Derived Average Glucose) formula validated in clinical trials. The BAC (blood alcohol content) calculator uses the Widmark formula with sex-specific distribution constants. The child height predictor uses the Khamis-Roche method (parent-height-based regression).

HSA contribution limits and IRS rules are updated to current-year figures (IRS Publication 969). Sleep duration recommendations follow the National Sleep Foundation consensus. Health calculators here are intended for general wellness and planning. Nothing in this category constitutes medical advice. Specific symptoms, medication decisions, or treatment plans require evaluation by a licensed physician — these calculators are a starting point for conversation, not a substitute.