BMI Calculator
Calculate your Body Mass Index (BMI) in metric or imperial units. Get your BMI value, weight category, BMI Prime, and healthy weight range for your height.
What your BMI result means
Your BMI score places you into one of four categories used by the CDC and most US doctors.
| BMI Range | Category | What It Signals |
|---|---|---|
| Below 18.5 | Underweight | May indicate nutritional gaps or low muscle mass |
| 18.5 – 24.9 | Healthy weight | Associated with the lowest health risk for most adults |
| 25.0 – 29.9 | Overweight | Moderate increased risk for metabolic conditions |
| 30.0 and above | Obese | Higher risk of diabetes, heart disease, and joint issues |
These ranges apply to adults aged 20 and older. Children, teens, and some ethnic groups use different thresholds.
BMI categories explained
Underweight (below 18.5)
A BMI under 18.5 can indicate poor nutrition, low bone density, or muscle loss.
It does not always mean poor health. Some people are naturally lean with healthy bloodwork and normal body fat levels.
Healthy weight (18.5 – 24.9)
This range is associated with the lowest risk of cardiovascular disease, type 2 diabetes, and metabolic syndrome in large population studies.
It is a statistical target, not a guarantee of good health.
Overweight (25.0 – 29.9)
Falling in this range does not automatically indicate a health problem.
Muscle mass, bone density, and fat distribution all affect what this number means for you specifically.
Obese (30.0 and above)
Obesity is divided into three classes:
- Class 1: 30.0 to 34.9
- Class 2: 35.0 to 39.9
- Class 3: 40.0 and above (sometimes called severe obesity)
Each class carries progressively higher risk. A doctor will typically look at additional markers before recommending a treatment plan.
Who should interpret BMI differently
The standard adult BMI chart does not apply equally to everyone.
Children and teens (ages 2–19)
BMI is still measured, but compared against age- and sex-specific growth charts. The four-category system above does not apply.
Asian Americans
Research cited by the American Heart Association shows that health risks increase at lower BMI levels for people of Asian descent. Many clinicians use an overweight threshold of 23.0 instead of 25.0.
Older adults (65+)
A BMI in the 25.0 to 27.0 range may actually be protective for older adults. Age-related muscle loss makes the standard cutoffs less reliable.
Athletes and highly active people
High muscle mass can push BMI into the "overweight" range even at low body fat percentages. BMI is not an accurate tool for this group.
What BMI does not measure
BMI is a ratio of weight to height. That is all it is.
It cannot tell you:
- How much of your weight is fat vs. muscle
- Where your body stores fat (belly fat is riskier than fat elsewhere)
- Your metabolic health, blood sugar levels, or cholesterol
- Whether you are gaining muscle or losing fat over time
A 2016 study in the International Journal of Obesity found that 54 million Americans classified as overweight or obese by BMI were metabolically healthy by clinical blood markers.
Use BMI as a starting screen, not a final answer.
Other measurements worth tracking alongside BMI
| Measurement | What It Shows | Healthy Target (US Adults) |
|---|---|---|
| Waist circumference | Abdominal fat level | Under 35 in (women), under 40 in (men) |
| Waist-to-height ratio | Central obesity risk | Below 0.5 for most adults |
| Body fat % | Actual fat vs. lean mass | Varies by age and sex |
| Blood pressure | Cardiovascular risk | Below 120/80 mmHg |
Your doctor typically reviews BMI alongside these, not in isolation.
When to talk to a doctor about your BMI
A single BMI number does not require a medical visit. But these situations do:
- BMI below 18.5 with unintentional weight loss
- BMI of 30.0 or above, especially with high blood pressure or blood sugar
- BMI in the healthy range but waist over 35 inches (women) or 40 inches (men)
- Rapid BMI change (up or down) in a short period
- Uncertainty about whether your score reflects muscle, fat, or fluid
A physician can pair your BMI with bloodwork and other markers to give you a real, individualized risk picture.
Frequently Asked Questions
What is a healthy BMI for women in the US?
The CDC defines 18.5 to 24.9 as healthy for adult women. Asian American women face elevated risk above 23.0. Age and body composition affect how that number should be interpreted.
What is a healthy BMI for men?
The same range applies: 18.5 to 24.9. Men with high muscle mass may register as overweight at 25+ without excess body fat. Waist circumference under 40 inches is a useful secondary check.
Is BMI accurate for athletes?
No. Muscle is denser than fat, so athletes with very low body fat often register as overweight or obese by BMI. Body fat percentage via DEXA scan is more accurate for athletic populations.
What BMI is considered obese by US standards?
A BMI of 30.0 or above is classified as obese by the CDC. This is split into three classes, with Class 3 (40.0+) carrying the highest associated health risk.
How often should I check my BMI?
Every 6 to 12 months is reasonable for most adults. Checking too often creates noise since BMI does not reflect short-term shifts in muscle gain, water retention, or food weight.
Does BMI differ for older adults?
Yes. Evidence suggests that a slightly higher BMI (25.0 to 27.0) may be protective for adults over 65 due to age-related muscle loss. The standard categories are less precise for this group.