Adult BMI calculator
Use height and weight to calculate body mass index. It is one screening measure, not a diagnosis or a guide to how long you should fast.
Enter your measurements
For adults age 20 and older. This page uses CDC adult categories. For ages 2–19, use the CDC child and teen calculator. Do not use this calculator during pregnancy or if you have, or think you may have, an eating disorder.
Your BMI result
The number is rounded to one decimal place. The category uses the unrounded value, so a result very close to a boundary may round to the next category’s starting number.
BMI cannot tell whether fasting is safe or suitable for you. A healthcare professional can put this result in context.
What this number can and cannot tell you
- BMI relates weight to height. It does not directly measure body fat or distinguish fat from muscle and bone.
- Interpretation needs context, including medical history, body composition, and other health measures. Standard categories alone cannot describe everyone’s individual risk.
- Pregnancy, conditions that affect height, and other circumstances may make this tool unsuitable. If you are unsure whether it applies to you, ask a qualified healthcare professional.
- A BMI result does not prescribe an eating window, fasting duration, calorie intake, or weight goal.
How BMI is calculated
BMI = weight in kilograms ÷ (height in metres × height in metres)
For example, 70 kg and 1.70 m gives 70 ÷ 2.89 = 24.2 when rounded. Imperial measurements are converted first: 1 inch = 0.0254 metres and 1 pound = 0.45359237 kilograms.
References checked October 4, 2026. This page follows the CDC’s 20+ age framework; the linked NHS service uses its own 18+ framework.