About HealthCalc Hub

Purpose

Each page gives the formula in plain words, an example with real numbers and answers to common questions. The aim is for a visitor to see how a number was reached, not only the number.

Methodology and sources

Every calculator runs in the browser on the numbers entered. Nothing typed is sent anywhere or saved. These are the formulas behind each one.

• BMI. Weight in kilograms divided by height in meters squared. For adults aged 20 and over the pages use the standard bands from the CDC and the World Health Organization: under 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight and 30 or more is obesity. For ages 2 to 19 the pages score BMI against the CDC 2000 growth charts for the child's age and sex (Kuczmarski and colleagues), using the L, M and S values the CDC publishes. The percentile cutoffs are the CDC's: under the 5th is underweight, the 5th to under the 85th is a healthy weight, the 85th to under the 95th is overweight and the 95th or more is obesity.
• Calories. Resting calories use the Mifflin-St Jeor equation (Mifflin and colleagues, American Journal of Clinical Nutrition, 1990): 10 times kilograms plus 6.25 times centimeters minus 5 times age, then plus 5 for males or minus 161 for females. Daily calories multiply that by an activity factor from 1.2 to 1.9.
• Body fat. The US Navy circumference method (Hodgdon and Beckett, 1984), which estimates body fat from height, neck and waist, plus hip for females. Results are grouped into the American Council on Exercise categories.
• Ideal weight. The Devine (1974), Robinson (1983) and Miller (1983) formulas. Each adds a set number of kilograms for every inch over 5 feet. The Devine formula was first written for drug dosing. These formulas are rules of thumb, not health targets.
• Pregnancy. Naegele's rule: the due date is 280 days after the first day of the last period, or 266 days after conception.
• Water. 35 milliliters per kilogram of body weight plus 350 milliliters for every 30 minutes of exercise. This is a common rule of thumb, not a medical standard.

What the calculators do and do not do

The calculators turn the numbers entered into an estimate using the formulas above. They do not diagnose anything and do not know a person's medical history. They cannot say what is right for a particular body. Formulas like these are built on averages. A single person can sit well away from the average. BMI cannot tell muscle from fat. The Navy method depends on how carefully the measurements are taken. A calorie estimate is a starting point to adjust against what body weight actually does.

HealthCalc Hub is not medical advice and its builder, Aaron Kapp, is not a health professional. The results are information. A doctor or other qualified health professional is the right person to ask about decisions that affect health.