No. It's a good, cheap population screen and a reasonable starting point for most people. It just shouldn't be the only measure, especially for very muscular or older individuals.

What's a better single measurement?

Waist-to-height ratio is a strong, simple option: keep your waist under half your height. It captures abdominal fat risk that BMI misses.

Does BMI work for children?

Not with adult categories. For children, BMI is read against age-and-sex percentile charts, because a healthy BMI changes as they grow.

Do BMI cutoffs vary by ethnicity?

Somewhat. Health bodies use lower overweight thresholds for some Asian populations, because health risks can appear at a lower BMI. Local guidelines reflect this.

Is BMI Reliable? The Limitations of Body Mass Index

Published 6/9/2026 · 2 min read · Health calculators

Sofia Nunes — Health & wellness writer at Allin

Nutrition · Hydration

Checked against 2 sources

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In short

BMI (weight divided by height squared) is a fast, free way to screen populations, but it does not measure body fat directly. It can misclassify muscular athletes as "overweight" and mask low muscle in older adults, and it ignores where fat sits — belly fat is riskier than hip fat. Use BMI as a starting point, then look at waist size, body-fat percentage and overall health rather than trusting one number.

A person in sportswear standing on a bathroom scale, seen from the knees down. — SHVETS production · Pexels · Pexels

BMI is a quick screen, not a diagnosis. Learn what it misses — muscle, fat distribution, age — and what to check alongside it.

It doesn't tell muscle from fat

BMI only knows your weight and height. A lean, muscular person can weigh a lot and land in the "overweight" range despite low body fat, while someone with little muscle can have a normal BMI yet carry unhealthy fat. That's why athletes and older adults are the classic cases where BMI misleads.

It ignores where fat sits

Two people with the same BMI can have very different risk. Fat around the abdomen (visceral fat) is more strongly linked to heart and metabolic disease than fat on the hips and thighs. A simple waist measurement, or waist-to-height ratio, captures this that BMI cannot.

Use it, but don't stop there

BMI is still a useful, cheap first screen — quick to calculate and reasonable across whole populations. Treat a result outside the normal range as a prompt to look closer, not a verdict. Pair it with waist size, body-fat estimate and how you actually feel and function.

Worked with our own calculator

BMI calculator

Given

Weight (kg): 70
Height (cm): 175

Result

BMI: 22.857

These figures are produced by the calculator below, not typed in by hand — they are recomputed whenever the tool changes.

Run it on your own figures →

Frequently asked questions

Is BMI useless then?: No. It's a good, cheap population screen and a reasonable starting point for most people. It just shouldn't be the only measure, especially for very muscular or older individuals.
What's a better single measurement?: Waist-to-height ratio is a strong, simple option: keep your waist under half your height. It captures abdominal fat risk that BMI misses.
Does BMI work for children?: Not with adult categories. For children, BMI is read against age-and-sex percentile charts, because a healthy BMI changes as they grow.
Do BMI cutoffs vary by ethnicity?: Somewhat. Health bodies use lower overweight thresholds for some Asian populations, because health risks can appear at a lower BMI. Local guidelines reflect this.

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For general information only — not medical advice. Consult a healthcare professional for personal guidance.

Sources

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