Calculate your BMI
- BMI compares your weight with your height. For most adults, a healthy BMI is 18.5 to 24.9.
- If your family background is South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean, health risks start at a lower BMI: 23 for overweight and 27.5 for obesity.
- Adding your waist measurement gives a fuller picture — aim to keep your waist below half your height.
- Medical weight-loss support is usually considered from a BMI of 30, or 27 with a weight-related condition (2.5 points lower for the backgrounds above).
How BMI is calculated
BMI is your weight in kilograms divided by your height in metres, squared. For example, someone who weighs 80 kg and is 1.75 m tall has a BMI of 80 ÷ (1.75 × 1.75) = 26.1. The calculator above does the maths for you and converts feet, inches, stones and pounds automatically.
BMI ranges for adults
| Category | Standard range | Lower thresholds* |
|---|---|---|
| Underweight | Below 18.5 | Below 18.5 |
| Healthy weight | 18.5 – 24.9 | 18.5 – 22.9 |
| Overweight | 25 – 29.9 | 23 – 27.4 |
| Obesity | 30 – 39.9 | 27.5 and above |
| Severe obesity | 40 and above | — |
*Used by NICE for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background. Why the thresholds are lower.
What your result does — and doesn't — tell you
BMI is a quick, reliable way to screen for weight-related health risk across large groups of people, but it has blind spots for individuals:
- Muscle: muscle weighs more than fat, so athletes and people who lift weights can have a high BMI with little body fat.
- Age: older adults often lose muscle, so their BMI can look healthy while body fat is high.
- Fat distribution: BMI cannot show whether fat is stored around your organs, which carries the most risk. Your waist-to-height ratio fills that gap.
- Pregnancy and under-18s: BMI is not used in pregnancy, and children are assessed with growth charts instead.
Read more in What is BMI and what does it tell you?
If your BMI is above the healthy range
You do not need to reach the healthy range to feel the benefits. Losing 5–10% of your body weight can lower blood pressure, improve blood sugar and cholesterol, and ease pressure on your joints. Small changes you can sustain — more protein and fibre, regular activity, better sleep — are the foundation.
If you have tried lifestyle changes without lasting results, a medical weight-loss programme may help. It is usually considered for adults with a BMI of 30 or more, or 27 or more with a weight-related condition. See who is eligible for medical weight loss and how our consultation works.
Not sure if medical weight loss is right for you?
Our free online assessment takes about five minutes. A GPhC-registered prescriber reviews it and only recommends treatment if it is safe and suitable for you.
Start the free assessmentFrequently asked questions
Is this BMI calculator suitable for children?
No. For under-18s, BMI is compared against growth centile charts for their age and sex. Speak to your GP or school nurse if you are concerned about a child’s weight.
Why are the thresholds lower for some ethnic groups?
People of South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean family backgrounds tend to develop type 2 diabetes and heart disease at a lower BMI. NICE therefore recommends 23 for overweight and 27.5 for obesity.
What BMI do I need for medical weight-loss treatment?
Prescription weight-loss treatment is generally considered for adults with a BMI of 30 or more, or 27 or more with a weight-related condition such as type 2 diabetes or high blood pressure. Thresholds are usually 2.5 points lower for the backgrounds above. A prescriber makes the final decision after a full assessment.
Do you store my results?
No. The calculator runs in your browser and does not send your measurements to us.
This page is general health information. It does not replace advice from your GP or another healthcare professional who knows your history. If you have symptoms that worry you, contact your GP or NHS 111; in an emergency call 999. Prescription treatment is only supplied after an assessment by a registered prescriber.