Use the right age framework
This calculator uses CDC adult categories for ages 20 and older. Children and teens need growth-based assessment instead.
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PERSPECTIVE
Adult BMI calculator
Calculate adult BMI and understand its limits.
Your BMI, in context
An adult screening category with its limitations.
Ready when you are.General information and estimates, not medical advice.
Use your result.
Separate screening from diagnosis
BMI is one screening measure. It cannot distinguish fat from muscle or establish your health on its own.
Read context before changing behaviour
Individual interpretation can differ. The NHS considers factors including ethnic background; a clinician can consider other information alongside BMI.
BEHIND THE NUMBERSMethod & trusted reading
A number.
Not your whole story.
Body mass index relates weight to height. This tool uses CDC adult categories for ages 20 and older.
The formula
BMI = weight (kg) ÷ height (m) squared. For example, 70 kg at 1.75 m gives approximately 22.86. Categories use the unrounded value, even when the displayed value is close to a boundary.
Adult categories
Below 18.5: underweight. From 18.5 to below 25: healthy weight. From 25 to below 30: overweight. From 30: obesity. CDC subdivides obesity at 35 and 40. These are screening categories, not diagnoses.
The bigger picture
BMI cannot distinguish muscle from fat or show fat distribution. Interpretation can vary with ethnic background, age, health, and circumstances. The NHS considers additional context. This tool does not cover pregnancy or pediatric growth.
Formula references
Documented 9 November 2026. No clinical review is claimed.
Read further.
Original research and official guidance. References do not imply endorsement of HandyShelf.
OFFICIAL CALCULATOR
Compare with the CDC adult calculator ↗
The official tool explains the adult categories and their role in screening.
Centers for Disease Control and PreventionOFFICIAL EXPLAINERWhat BMI can and cannot tell you ↗
Answers on body composition, limitations, and interpreting BMI alongside other information.
Centers for Disease Control and PreventionNHS ASSESSMENTAn assessment with more context ↗
The NHS adult calculator explains additional considerations, including ethnic background and situations where BMI tools are unsuitable.
National Health ServiceQuick questions.
Is BMI a diagnosis?
No. It is a screening measure. It cannot establish your health without other information and assessment.
Can children use this?
No. Children and teenagers need age- and sex-specific growth assessment. This tool is for adults 20 and older.
Why does a rounded number seem near another category?
The displayed value has two decimals. The category uses the full unrounded number.