What Is a Healthy BMI? Chart, Formula and Examples

A healthy BMI for adults is between 18.5 and 24.9. BMI (body mass index) is your weight in kilograms divided by your height in metres squared. Under 18.5 counts as underweight, 25 to 29.9 as overweight, and 30 or more as obese. You can check yours in seconds with the BMI Calculator.

What do the BMI categories mean?

The World Health Organization uses these adult categories:

BMI	Category
Under 18.5	Underweight
18.5 – 24.9	Healthy weight
25 – 29.9	Overweight
30 or more	Obese

Health risk rises gradually as BMI moves away from the healthy range, not suddenly at one line. Some health services use lower thresholds for people of South Asian, Chinese, Middle Eastern, Black African or African-Caribbean background, because health risks such as type 2 diabetes can start at a lower BMI. The NHS, for example, uses 23 and 27.5 as the overweight and obesity thresholds for these groups.

How do I calculate my BMI?

The formula is simple:

BMI = weight (kg) ÷ height (m)²

Worked example: someone who weighs 70 kg and is 175 cm tall.

1. Height in metres: 1.75
2. Height squared: 1.75 × 1.75 = 3.0625
3. BMI: 70 ÷ 3.0625 = 22.9, a healthy weight.

In pounds and inches the formula is 703 × weight (lb) ÷ height (in)². A person who is 5 ft 9 in (69 in) and 154 lb has 703 × 154 ÷ 4,761 = 22.7.

The BMI Calculator does this for you in metric (cm, kg) or US units (ft, in, lb), shows your category on a coloured scale and gives the healthy weight range for your height.

What is a healthy weight for my height?

Because BMI is based on height, you can turn the healthy range around to find a target weight. For a height of 175 cm:

• 18.5 × 3.0625 = about 56.7 kg
• 24.9 × 3.0625 = about 76.3 kg

So anywhere from roughly 57 to 76 kg is in the healthy BMI range at that height. The calculator shows this range automatically. For a second opinion, the Ideal Weight Calculator adds four classic ideal-weight formulas.

When is BMI misleading?

BMI is a quick screening number, not a diagnosis. It doesn't measure body fat directly, so:

• Muscular people may be called overweight even with low body fat.
• Older adults can have a "normal" BMI but low muscle and more fat.
• Where you carry fat matters. Fat around the belly is more closely linked to heart disease and diabetes than weight alone.

That's why doctors often pair BMI with waist size. You can check that with the Waist-to-Hip Ratio Calculator or estimate fat directly with the Body Fat Calculator. Our guide on measuring body fat at home explains how.

What should I do if my BMI is too high or too low?

If your BMI is over 25, a slow, steady loss of about 0.5 kg (1 lb) a week is a realistic goal for most people. Even a 5–10% loss can improve blood pressure and blood sugar. Start by finding your calorie needs with the Calorie Calculator.

If your BMI is under 18.5, it's worth talking to a doctor, especially if you've lost weight without trying. Being underweight can be linked to poor nutrition, thyroid problems or other conditions.

Pregnant women, children and teenagers shouldn't use adult BMI categories. Ask a doctor or midwife about healthy weight gain in pregnancy.

Common mistakes when checking BMI

• Using height in centimetres instead of metres in the formula (it gives a tiny number).
• Measuring height in shoes, or weight in heavy clothes.
• Treating 25.0 as "unhealthy" and 24.9 as "healthy": it's a scale, not a cliff edge.

Check your BMI now

Use the free BMI Calculator. It works on any phone or computer, needs no sign-up, and runs entirely in your browser, so your height and weight are never sent anywhere.