Health calculator questions, answered.

Mifflin-St Jeor (1990). In validation studies it lands closest to measured resting energy expenditure for most adults, which is why the Academy of Nutrition and Dietetics recommends it over the older Harris-Benedict equation. We show both when the difference matters. Your real needs can still vary by 10-15% either way; treat the output as a starting point and adjust from two weeks of real data.

They estimate population averages, not you. A TDEE result within 10% of reality is a good outcome. The useful move is not chasing a perfect number: it is picking one formula, tracking for two weeks, and adjusting. The formula gives you a starting point. Your body gives you the rest.

It is a screening tool, not a diagnosis. BMI does not separate muscle from fat, so athletes often read as overweight while their body fat is low. For most people it is a reasonable first check; pair it with waist-to-hip ratio or body fat percentage before drawing conclusions. WHO categories: under 18.5 underweight, 18.5-24.9 normal, 25-29.9 overweight, 30+ obese.

Per the American Council on Exercise: for men, fitness is 14-17% and average is 18-24%; for women, fitness is 21-24% and average is 25-31%. Essential fat (the minimum for health) is 2-5% for men and 10-13% for women. Method matters: calipers and smart scales can be off by several points, so track the trend, not the single reading.

Research supports 300-500 kcal per day below maintenance for most adults: enough to lose roughly 0.5-1 lb per week while keeping muscle and staying sane. Bigger deficits backfire through muscle loss and rebound. If that number surprised you, you're not alone.

The RDA is 0.8 g per kg of body weight, but that is a minimum to prevent deficiency, not an optimum. Active adults do better at 1.2-1.6 g/kg, and lifters at 1.6-2.2 g/kg per the International Society of Sports Nutrition (2017). Spread it across meals; your body is not a spreadsheet, but the math still helps.

No. The A1C, GFR, BAC, and blood pressure tools are educational conversions of published clinical formulas. They are not diagnostic tools, they do not replace laboratory tests, and you should never adjust medication based on a calculator result. Bring the numbers to your physician; that conversation is the whole point.

Any time a number drives a medical decision: starting a diet with a health condition, unusual readings (blood pressure, resting heart rate), pregnancy questions, or anything involving medication. Calculators are for context and curiosity. Care belongs to professionals who can see the whole picture.