Is BMI accurate for athletes?

High muscle mass can elevate BMI without indicating excess fat, so BMI may misclassify athletes.

Does BMI change with age?

The formula stays the same, but body composition changes; older adults often have higher fat at the same BMI.

How often should I check my BMI?

Checking every few months is adequate unless you’re under active weight‑loss or medical supervision.

BMI Ranges Explained: Chart, Health Risks & FAQ

Body-Mass Index (BMI) is a quick way to gauge whether your weight is in a healthy range for your height. Enter your stats in our BMI Calculator, then use the chart below to understand what the number means for your health.

What is BMI?

BMI (Body Mass Index) is a widely used screening tool to categorize weight status and potential health risks. It is calculated using your weight and height, and helps you understand if you are underweight, normal weight, overweight, or obese. While simple, it is not a direct measure of body fat.

Official BMI Classification Chart

BMI	Category
< 18.5	Underweight
18.5 – 24.9	Normal weight
25 – 29.9	Overweight
30 – 34.9	Obesity I
35 – 39.9	Obesity II
≥ 40	Obesity III

BMI Health Risks by Category

Underweight – potential nutrient deficiency, bone loss.
Normal weight – lowest overall health risk.
Overweight – elevated risk of hypertension, pre-diabetes.
Obesity (all classes) – increased risk of type 2 diabetes, heart disease, sleep apnea, certain cancers.

Limitations of BMI (and what to use instead)

BMI does not account for muscle mass, bone‑fat distribution, age, sex, or ethnicity. For a more complete picture, consider measuring waist-to-height ratio, body-fat percentage, or consulting a healthcare professional for personalized advice.

How to Improve Your BMI (and Health)

Create a slight calorie deficit (or surplus if underweight).
Combine strength training with cardio.
Prioritise whole foods rich in fibre and protein. Also well balanced meals are key.
Sleep 7–9 hours per night; manage stress.
Consult a healthcare professional before major lifestyle changes.

Frequently Asked Questions (FAQ)

Is BMI accurate for athletes?: Not always. High muscle mass can inflate BMI, categorising athletes as “overweight” even with low body‑fat.
Does BMI change with age?: BMI formula is constant, but body composition shifts with age. Older adults may have more fat at the same BMI.
How often should I check my BMI?: Every few months is sufficient unless you’re tracking rapid weight changes under medical guidance.
How do I convert Celsius to Fahrenheit?: See our Celsius vs Fahrenheit Cooking Guide for conversion tips and charts.

Sources: World Health Organization BMI Fact Sheet; U.S. CDC “About Adult BMI.

Last updated 15 Jun 2025