Health
BMI, due dates, calories and water. Estimates, never a diagnosis.
Estimates, and the word is chosen carefully. Every figure here comes from a published population formula applied to numbers you typed, not from anything measured about you. A calculator can tell you what the Mifflin–St Jeor equation says about a body of your height and weight. It cannot tell you whether that is true of yours, and none of these is a diagnosis or a substitute for asking someone qualified.
Which formula produced the number
The energy tools chain together. BMR is the resting figure, TDEE multiplies it by an activity factor between 1.2 and 1.9, and the calorie and macro calculators split that total into a daily target and then into grams. Start at BMR if you want to understand the number and at TDEE if you only want it. The pregnancy set — due date, pregnancy progress and ovulation — all count from the first day of the last period, so they agree with each other and may disagree with a dating scan. The scan wins.
Ring, bra and shoe sizing are lookup charts against a measurement rather than formulas, which is why they hand back a size and the band either side of it. Body fat uses the US Navy circumference method and is honest about its roughly three-point spread. Pace and one-rep max are training maths and sit here rather than under Maths because the units are athletic and the caveats are physiological.