Fitly PulseBMI Explained: What It Does and Doesn’t Tell You
Body mass index (BMI) is one of the most widely used health screening numbers. It is quick and free to calculate, but it is only a rough screening tool. This guide explains how it works and where it falls short.
How BMI is calculated
BMI = weight (kg) ÷ height (m)². For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.
WHO adult categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal range |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Our calculator uses these standard categories for adults.
What BMI does not tell you
- Muscle vs fat. BMI cannot tell them apart, so a muscular person can be labelled “overweight” despite low body fat.
- Where fat is stored. Fat around the waist carries more health risk than fat elsewhere, but BMI does not measure it.
- Age and sex. Body composition changes with age, and men and women carry fat differently.
- Children and teens. They need age- and sex-specific growth charts, not adult categories.
BMI and Asian populations
Research has shown that many Asian populations have a higher risk of type 2 diabetes and cardiovascular disease at lower BMI values than European populations. A WHO expert consultation in 2004 suggested additional public-health action points at BMI 23 (increased risk) and 27.5 (high risk). Several national guidelines in Asia use lower cut-offs. If you are of Asian descent, a BMI in the upper part of the “normal” range may still deserve attention, so discuss it with your doctor.
Better together: other measurements
- Waist circumference or waist-to-height ratio (a common guideline is to keep your waist below half your height)
- Blood pressure, blood sugar and cholesterol from routine health checks
- Fitness and daily habits: activity, sleep, diet quality
The bottom line
Use BMI as a starting point for a conversation, not a verdict. If your result is outside the normal range, or you are worried about your weight, a healthcare professional can look at the full picture.
Try it yourself — the free Fitly Pulse tracker runs these calculations in your browser. No account needed.
Open the free trackerReferences
- World Health Organization. Obesity and overweight fact sheet. who.int/news-room/fact-sheets/detail/obesity-and-overweight
- WHO Expert Consultation (2004). Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet. PubMed 14726171