Question 1

What BMI is considered healthy by the NHS?

Accepted Answer

The NHS defines a healthy BMI as between 18.5 and 24.9. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese. These bands apply to most adults aged 18 and over.

Question 2

Is BMI accurate?

Accepted Answer

BMI is a useful population-level screening tool but is not a direct measure of body fat. It can overestimate health risk for very muscular people and underestimate it for those with high body fat but low muscle mass. Age, ethnicity and where fat is carried also matter. The NHS uses it as one indicator alongside waist measurement and other factors.

Question 3

What BMI is healthy for women vs men?

Accepted Answer

The NHS uses the same BMI bands for both men and women: healthy is 18.5–24.9, overweight is 25–29.9, obese is 30 and above. However, women naturally carry more body fat than men at the same BMI, so some clinicians use additional measures for a fuller picture.

Question 4

How do I calculate BMI manually?

Accepted Answer

BMI = weight in kg ÷ (height in metres × height in metres). For example, 75 kg and 1.75 m tall: 75 ÷ (1.75 × 1.75) = 75 ÷ 3.0625 = 24.5.

Question 5

What is a healthy weight for my height?

Accepted Answer

A healthy BMI of 18.5–24.9 translates to different weight ranges depending on height. For a 5 ft 7 in (170 cm) person, healthy weight is roughly 53–72 kg (8 st 5 lb to 11 st 4 lb). For 5 ft 10 in (178 cm), it is roughly 58–79 kg (9 st 2 lb to 12 st 6 lb). The calculator shows your exact healthy weight range.

Question 6

Does BMI apply to children?

Accepted Answer

Standard adult BMI bands do not apply to children and teenagers. For under-18s the NHS uses age- and sex-specific centile charts, since healthy body fat varies significantly during development. This calculator is designed for adults aged 18 and over.

Question 7

What BMI is considered obese?

Accepted Answer

A BMI of 30 or above is classified as obese by the NHS. This is broken down further into Class 1 (30–34.9), Class 2 (35–39.9), and Class 3 or severe obesity (40 and above). A BMI of 25–29.9 is overweight, which also carries increased health risks.

Question 8

Is BMI different for people of South Asian or Black heritage?

Accepted Answer

Yes — NICE guidance suggests lower BMI thresholds for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds. For these groups, overweight may start at BMI 23 and obesity at BMI 27.5, as health risks appear at lower BMI values.

BMI Calculator UK — Body Mass Index and NHS Weight Bands