What Is a Healthy BMI?

What BMI range is healthy for adults?

A BMI of 18.5 to 24.9 is the healthy (or "normal") range for adults 20 and older, according to both the World Health Organization (WHO) and the CDC. Body mass index (BMI) is a ratio of weight to height squared. It does not measure fat directly, but across large populations it tracks body fat well enough to work as a quick screening number.

The categories below are the standard adult ones. Our BMI calculator uses them for anyone 20 or older and shows the band you fall in, plus how many pounds or kilograms would bring you to the nearest edge of the healthy range.

What is the BMI formula?

BMI equals weight in kilograms divided by height in meters squared. In US units, multiply weight in pounds by 703, then divide by height in inches squared. The 703 is a conversion factor: it turns pounds and inches into the same kg/m² number the metric formula gives.

Metric example: someone 165 cm tall who weighs 60 kg has a height of 1.65 m. Square it to get 2.7225, then divide 60 by 2.7225. The BMI is 22.0, inside the healthy range.

Imperial example: someone 5 feet 10 inches tall (70 inches) who weighs 160 pounds. Square the height to get 4,900. Multiply 160 by 703 to get 112,480, then divide by 4,900. The BMI is 23.0.

A third example above the range: 175 cm and 85 kg gives 85 ÷ 3.0625 = 27.8, which is overweight. For that height, the healthy range runs from 56.7 to 76.6 kg, so reaching a BMI of 25 would mean losing about 8.4 kg. All three results match what our calculator returns for the same inputs.

• Metric: BMI = weight (kg) ÷ height (m)²
• US: BMI = 703 × weight (lb) ÷ height (in)²
• BMI Prime = BMI ÷ 25, so a value above 1.0 means above the healthy upper limit

Is the BMI formula different for women?

No. Adult women and men use the same formula and the same categories. A woman who is 5 feet 4 inches tall and weighs 145 pounds has a BMI of 24.9, just inside the healthy range, exactly as a man of the same height and weight would.

What differs is what the number means. The CDC notes that at the same BMI, women tend to carry more body fat than men. That is why some body composition tools ask for sex even though BMI itself does not. If you want an estimate that accounts for sex, the body fat calculator uses tape measurements instead of weight alone. BMI also isn't used to judge weight during pregnancy; pregnancy weight gain targets are based on BMI before pregnancy.

What is a healthy weight for my height?

Multiply your height in meters squared by 18.5 and by 24.9 to get the healthy weight range in kilograms. The healthy weight calculator does this for you in pounds or kilograms. The table shows the range for common heights, using the BMI 18.5 to 25 boundaries our calculators use, with the midpoint at a BMI of 21.75.

Does a healthy BMI change with age?

For adults, no: the 18.5 to 24.9 range applies from age 20 onward, with no separate table for people in their 40s, 60s or 80s. For children and teens, yes: BMI is read against other children of the same age and sex, because body fat changes a lot as kids grow and differs between boys and girls.

The CDC compares a child's BMI with its growth charts and reports a percentile. A boy at the 70th percentile has a higher BMI than 70% of boys his age in the reference data. The CDC categories for ages 2 through 19 are shown below. Our BMI calculator gives the raw number for anyone under 20 but deliberately does not apply the adult labels; a pediatrician or the CDC's child and teen tool will plot the percentile.

What are the limits of BMI?

BMI only knows height and weight, so it cannot separate muscle from fat or show where fat sits. That leads to predictable errors in a few groups.

• Athletes and very muscular people: muscle is dense, so a lean weightlifter can score 27 or higher and be labeled overweight with little excess fat.
• Older adults: people tend to lose muscle and gain fat with age, so an older adult can have a normal BMI while carrying more body fat than a younger adult with the same number.
• Ethnicity: a 2004 WHO expert consultation found that many Asian populations face higher risk of type 2 diabetes and heart disease at BMIs below 25. It kept the international cut-offs but proposed extra public health action points at 23, 27.5, 32.5 and 37.5, and some countries use 23 as the overweight threshold.
• Fat location: fat around the abdomen carries more risk than fat on the hips and thighs, and BMI cannot see the difference.
• Pregnancy: BMI is not meant for use during pregnancy.

What should I check besides BMI?

Measure your waist. The NHLBI considers a waist above 40 inches for men or 35 inches for women a sign of higher risk for type 2 diabetes and heart disease, even when BMI is in the healthy range. Measure just above your hip bones, right after you breathe out.

Body fat percentage gives a more direct picture of composition; our guide on how to measure body fat explains the tape method and other options. Blood pressure, blood sugar and cholesterol tests from your doctor round out the picture. The ideal weight calculator shows several older clinical formulas, such as Robinson and Devine, that give a single target weight; for a 5 ft 4 in woman they range from 119.7 to 129.1 lb, all inside the BMI-based healthy range of 107.8 to 145.6 lb.

If your BMI is above the healthy range and you want to change it, our guide on how many calories to eat to lose weight covers the next step. The NHLBI says health professionals recommend losing 5% to 10% of your starting weight over about 6 months, and that even a 3% to 5% loss can lower triglycerides and blood sugar.