Is BMI accurate for athletes?

No. Muscle is denser than fat, so muscular people often read as 'overweight' despite low body fat. For them, body composition measures are far more useful.

What is a healthy BMI for older adults?

Slightly higher ranges — often up to around 27 — may be fine and even protective in older age. Ask a healthcare professional about your personal target.

Does BMI differ for men and women?

The adult ranges are the same for both, even though body composition differs. BMI does not account for sex, which is one of its known limitations.

What Is a Healthy BMI?

Published 11/13/2025 · 2 min read · Health calculators

Sofia Nunes — Health & wellness writer at Allin

Nutrition · Hydration

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In short

Body Mass Index (BMI) is your weight in kilograms divided by your height in metres squared. For most adults, 18.5–24.9 is the 'healthy' range, under 18.5 is underweight, 25–29.9 is overweight and 30+ is obese. A 70 kg person at 1.75 m has a BMI of 22.9. BMI is a quick screen, not a diagnosis — it ignores muscle, age and body composition.

Feet in socks standing on a digital bathroom scale, seen from above. — Andres Ayrton · Pexels · Pexels

BMI groups weight into ranges relative to height. Here's what counts as healthy, how to calculate it, and the limits of the number.

How BMI is calculated

Divide your weight in kilograms by your height in metres, squared. Someone who is 70 kg and 1.75 m tall computes 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9. If you use pounds and inches, multiply the result by 703 instead. The number itself is unitless — it only means something against the standard ranges.

The BMI ranges

The World Health Organization groups adult BMI into four bands: underweight below 18.5, healthy 18.5 to 24.9, overweight 25 to 29.9, and obese at 30 and above. These bands are the same for men and women, and they describe population risk rather than any single person's health.

What BMI misses

BMI only knows your weight and height, so it cannot tell muscle from fat. A muscular athlete can read as 'overweight' with very low body fat, while someone in the healthy range may carry excess fat and little muscle. It also says nothing about where fat sits — belly fat carries more risk — or about age and ethnicity, which shift the picture.

Use it alongside other measures

Treat BMI as one signal among several. Waist circumference, waist-to-height ratio and body fat percentage add the fat-distribution picture it lacks, and how you feel and move matters too. For anything beyond a rough check, a doctor or dietitian can read these together and tell you what, if anything, to act on.

Adult BMI categories (WHO)
BMI	Category
Below 18.5	Underweight
18.5–24.9	Healthy weight
25.0–29.9	Overweight
30.0 and above	Obese

Worked with our own calculator

BMI calculator

Given

Weight (kg): 63
Height (cm): 158

Result

BMI: 25.236

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 accurate for athletes?: No. Muscle is denser than fat, so muscular people often read as 'overweight' despite low body fat. For them, body composition measures are far more useful.
What is a healthy BMI for older adults?: Slightly higher ranges — often up to around 27 — may be fine and even protective in older age. Ask a healthcare professional about your personal target.
Does BMI differ for men and women?: The adult ranges are the same for both, even though body composition differs. BMI does not account for sex, which is one of its known limitations.

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This is general information, not medical advice. BMI is a screening tool, not a diagnosis — a healthcare professional can interpret it in the context of your age, muscle mass and overall health.

Sources

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