Health and fitness guides

Short, practical guides that explain what the numbers from our calculators mean. Each one has a direct answer, charts, a quiz, a checklist and links to the calculators it supports. Every figure has a named source.

Body composition

BMI limitations: what your BMI does and does not tell youWhat BMI measures, what it misses, and what to check alongside it.

Calories & weight loss

What is a safe calorie deficit?How big a calorie deficit can be, the limits we use, and who should check with a doctor first.

How we write guides

Guides explain, calculators calculate. Each guide links to the live calculators it supports, uses numbers only from named sources, and says when to speak with a doctor. Results and guides are for information only and are not medical advice. See our editorial policy and methodology.