HowToCalculateBMI.org

BMI and Health Risks

Written by the HowToCalculateBMI.org team Updated 2 min read

Checked against 5 cited sources

A higher BMI is linked with a higher risk of type 2 diabetes, high blood pressure, heart disease and stroke, among other conditions, and the risk rises through the obesity classes. Waist size changes the picture: at the same BMI, a waist over 40 inches (102 cm) for men or 35 inches (88 cm) for women adds risk. A low BMI has risks too. BMI shows risk for groups of people; it can't tell you your own health on its own.

On this page

Conditions linked with a higher BMI

The CDC and the WHO link a higher BMI with a higher risk of these conditions:12

  • Type 2 diabetes
  • High blood pressure and high cholesterol
  • Heart disease and stroke
  • Sleep apnea and breathing problems
  • Osteoarthritis, especially in the knees
  • Fatty liver disease and gallbladder disease
  • Several cancers

Risk by BMI and waist size

The US National Heart, Lung, and Blood Institute combines BMI with waist size to rank the risk of type 2 diabetes, high blood pressure and heart disease, compared with a healthy weight:3

BMI Waist at or under 40 in (men) / 35 in (women) Waist over 40 in (men) / 35 in (women)
25–29.9 Increased High
30–34.9 High Very high
35–39.9 Very high Very high
40 and above Extremely high Extremely high

Check your waist-to-height ratio.

Risks of a low BMI

A BMI under 18.5 can go with undernutrition, a weaker immune system, thinning bones (osteoporosis), and, in women, missed periods and fertility problems. In older adults especially, low weight or unintended weight loss is linked with poorer health. BMI for older adults.

What BMI can't show

Risk depends on much more than size: blood pressure, blood sugar, cholesterol, activity, smoking, sleep and family history all matter. Someone with a healthy BMI can still be at risk, and someone with a high BMI can be metabolically healthy. What BMI can and can't tell you.

Talk to a doctor if your BMI is 30 or more, or 25 to 29.9 with a large waist or other risk factors. They can check the numbers BMI can't show. When to see a doctor.

Frequently asked questions

At what BMI do health risks increase?

Risk starts to rise in the overweight range (25 to 29.9) and increases further through the obesity classes.3 For adults of Asian descent, risk rises at lower BMIs.4 Asian BMI.

Does losing weight lower the risk?

For people above the healthy range, losing even 5 to 10% of body weight can improve blood pressure, blood sugar and cholesterol.5 Talk to a doctor about what's right for you. When to see a doctor.

Sources

  1. CDC: consequences of obesity ↩

  2. WHO ↩

  3. NHLBI: classification of overweight and obesity ↩ ↩

  4. WHO expert consultation (2004), The Lancet ↩

  5. CDC: losing weight ↩

Written by

The HowToCalculateBMI.org team

We explain BMI in plain language, check every worked example with automated tests, and keep each page up to date with current guidelines.

How we write and check our pages

Kept up to dateLast updated October 9, 2026

This page is for education and is not medical advice. A doctor can assess your own health risks, which depend on much more than BMI.

When to See a Doctor About BMI When a BMI result is worth raising with a doctor: low or high BMI, unexplained weight change, kids' percentiles and pregnancy. Plus questions. Read BMI Chart Find your BMI on an interactive chart or a printable table by height and weight, in feet and pounds or cm and kg, color-coded by category. Read BMI Categories Adult BMI categories: underweight below 18.5, healthy 18.5–24.9, overweight 25–29.9, obesity from 30. What each means, plus kids' ranges. Read