Health & Body Composition Calculators

How these metrics fit together

BMI, BMR, TDEE, and body fat percentage all sound like variations on the same theme — they all use weight and height as inputs — but they answer four very different questions. BMI asks whether your weight is in a typical range for your height. Body fat percentage asks how much of that weight is fat versus everything else. BMR asks how many calories your body burns at complete rest. TDEE asks how many calories you actually burn in a normal day, including movement and digestion. Treating any one as a stand-in for the others is the single most common mistake in body composition tracking.

For most adults, the practical workflow looks like this: BMI gives a 30-second sanity check. If something looks off, body fat percentage clarifies what kind of weight you're carrying. BMR sets the calorie floor you should not eat below. TDEE sets the maintenance target you plan meals around. The four together make a complete picture; any one alone leaves a gap.

All five health calculators

• BMI Calculator

  Body Mass Index — a 30-second weight-vs-height screening number. WHO and CDC categories included.

• BMR Calculator

  Basal Metabolic Rate using the Mifflin-St Jeor equation. The calorie floor your body burns at complete rest.

• TDEE Calculator

  Total Daily Energy Expenditure — your maintenance calories based on BMR and activity level. The number you actually plan meals around.

• Body Fat Calculator

  U.S. Navy circumference method. Tracks body composition more accurately than BMI when you only have a tape measure.

• Age Calculator

  Exact age in years, months, days. Handles leap years and month-boundary edge cases that naive subtraction misses.

Recommended reading

• BMI vs BMR vs TDEE: Which Should You Use to Track Your Health?

  Three metrics, one body. A decision tree for picking the right number with the equations and references explained.

Editorial standards for this category

Health metrics are YMYL (Your Money or Your Life) content under Google's quality guidelines. We hold this category to a higher review bar than our other tools: every formula is implemented from the original published paper, every cut-off comes from a primary regulatory or clinical source (WHO, CDC, NIH, or a peer-reviewed journal), and every limitation noted in the original literature is surfaced in the explainer section of the tool. We do not give medical advice and explicitly note where a calculator's assumptions break down (athletes with high muscle mass, older adults with sarcopenia, pregnancy, certain ethnicities with shifted BMI risk profiles).