Overweight vs obesity: what’s the difference?

The two words are often used as if they mean the same thing, but health organisations draw a clear line between them. Obesity is the higher of the two.

For adults

• Overweight: BMI of 25 or more (this group includes people with obesity).
• Obesity: BMI of 30 or more.

“overweight is a BMI greater than or equal to 25; and obesity is a BMI greater than or equal to 30.”

So when WHO estimates that 45.2% of the world’s adults were overweight in 2024, that number includes the 16.4% living with obesity. That leaves about 28.8% who were overweight but did not have obesity.

Three classes of obesity

CDC splits adult obesity into class 1 (BMI 30 to under 35), class 2 (35 to under 40) and class 3, also called severe obesity (40 or more).

“Class 1 Obesity: 30 to less than 35 … Class 2 Obesity: 35 to less than 40 … Class 3 Obesity (Severe Obesity): 40 or greater”

For children and teens

For ages 5–19, overweight means BMI-for-age more than 1 standard deviation above the WHO Growth Reference median; obesity means more than 2 standard deviations above it.