Formula Hub

Naegele's Rule estimates a pregnancy due date by adding 280 days (40 weeks) to the first day of the last menstrual period, since gestational age is conventionally measured from LMP even though conception typically occurs about two weeks later. A cycle-length adjustment corrects for women whose cycles are longer or shorter than the standard 28-day assumption, since a longer cycle means ovulation (and conception) happens later.

Rather than using a single flat RDA figure (0.8 g/kg), this formula applies an evidence-informed multiplier that varies by both fitness goal and activity level, since athletic, weight-loss, and muscle-building populations need substantially more protein than a sedentary baseline to preserve or build lean mass. Additional flat or incremental bonuses account for higher protein needs in older adults and during pregnancy/lactation.

Calculating a target heart rate training zone actually involves two separate decisions: which formula to use for estimating Maximum Heart Rate (MHR), and then how to convert that MHR into an actual target zone. Haskell & Fox's "220 minus age" is the older, simpler, and most widely recognized MHR formula, but it was derived from a relatively small and non-representative sample. Tanaka's formula (208 − 0.7×age) is a more recent, research-validated alternative developed from a meta-analysis of a much larger dataset, and tends to be considered more accurate, particularly for older adults. Once an MHR estimate is chosen, the Karvonen method converts it into a target heart rate by factoring in resting heart rate (via Heart Rate Reserve) rather than just applying a flat percentage of MHR, which produces more personalized training zones for people with different fitness levels.

The Mifflin-St Jeor Equation calculates Basal Metabolic Rate (BMR) — the calories your body burns at complete rest — from weight, height, age, and gender. Multiplying BMR by an activity factor scales it up to Total Daily Energy Expenditure (TDEE), the actual number of calories burned per day including movement and exercise, which is the standard baseline for setting weight loss, maintenance, or gain calorie targets.

Waist-to-Height Ratio is a simple screening tool for central obesity, based on the guideline of keeping your waist circumference below half your height. Unlike BMI or Waist-to-Hip Ratio, it doesn't require separate male/female cutoffs, making it a more universally applicable single-threshold measure of cardiometabolic risk across genders, ages, and even ethnicities.

Waist-to-Hip Ratio is a simple ratio that indicates body fat distribution pattern — whether fat accumulates more around the abdomen ("apple" shape) or the hips and thighs ("pear" shape). A higher ratio indicates more central/visceral fat, which is strongly associated with increased cardiovascular and metabolic disease risk, following World Health Organization risk classification guidance.