BMI calculator

Large studies show lowest mortality rates between BMI 20-25, not 18.5-24.9. Being slightly overweight (25-27) shows similar mortality to "normal" weight. Being underweight (under 20) carries higher mortality risk than being moderately overweight.

Older adults often have lower muscle mass and higher body fat at the same BMI as younger adults. A 70-year-old with BMI 23 may be overfat, while a 25-year-old with BMI 27 may be muscular. Age-adjusted assessments are more accurate for older populations.

Despite its limitations, BMI remains common in insurance underwriting because it's cheap to calculate. Some policies charge higher premiums above BMI 30. This has led to calls for more nuanced health assessments that don't penalize muscular individuals.

In some conditions (heart failure, kidney disease, certain cancers), patients with higher BMIs actually have better survival rates. This "obesity paradox" challenges simple BMI-based health assumptions and suggests body composition matters more than weight alone.

No. BMI doesn't distinguish muscle from fat. Athletes, weightlifters, and anyone with above-average muscle mass will have misleadingly high BMIs. If you exercise regularly and have visible muscle definition, consider body fat percentage or waist circumference instead.

For most adults, 18.5-24.9 is the "normal" range, with lowest mortality risk around 20-25. But health depends on many factors BMI doesn't measure: fitness, diet quality, blood pressure, blood sugar, and family history. A fit person at BMI 27 may be healthier than a sedentary person at BMI 22.

Maybe, but focus on health behaviors rather than a number. Regular exercise, balanced nutrition, adequate sleep, and stress management matter more than achieving a specific BMI. Rapid weight loss to reach a BMI target can be less healthy than stable weight at a higher BMI.

It's simple, free, and correlates with health outcomes at a population level. For initial screening, it flags people who might benefit from further assessment. The problem is when it's used as the only metric or as a diagnosis. Good doctors use it as a starting point, not an endpoint.

Pediatric BMI uses age- and sex-specific percentiles, not adult cutoffs. This calculator targets adults; use growth charts or a pediatric-specific tool for kids.

Not as a standalone metric—weight gain guidelines are trimester-specific and individualized. Ask your obstetric provider how they want you to track changes.

Waist circumference, waist-to-hip ratio, blood pressure, lipids, glucose, strength, and how you feel day to day. Composition scans (DEXA) help if available, but are not required to improve health behaviors.

Some underwriting still references BMI bands. Laws vary by region and role. If you are muscular or pregnant, documentation from a clinician may matter—this page does not provide that.

BMI calculations don't change with age for adults—same formula for 25 or 75. But healthy BMI ranges may shift slightly: some research suggests slightly higher BMI (25-27) is associated with lower mortality in older adults. Muscle mass tends to decline with age, so maintaining weight means gaining fat unless you resistance train.

The BMI formula is the same for both sexes, but body composition differs—women typically have higher body fat percentage at the same BMI. A BMI of 24 might be 20% body fat for a man and 30% for a woman. That's one reason why BMI alone doesn't tell the full story.

Body composition is the ratio of fat mass to lean mass (muscle, bone, organs). Two people at the same BMI can have completely different body composition—one might be 15% body fat, the other 35%. Composition matters for health: high muscle mass protects metabolic health even at higher weight. BMI can't see this difference.

DEXA scans are gold standard but expensive. Bioelectrical impedance scales are affordable but less accurate. Skinfold calipers work if done consistently. For most people, waist circumference (measure at navel level) is simpler and correlates well with visceral fat—which matters more for health than total weight.

Compute BMI from recent height/weight, note category, then bring questions about waist measurement or labs to your appointment.

Switch units and confirm the category stays stable—helps classroom demos show the formula is equivalent across systems.

Pair a normal-BMI example with a high-muscle example at the same height to show why screening is not diagnosis.

Cite our methodology version when publishing population-level commentary so readers can reproduce your worked example later.

Some forms ask height/weight; BMI is a quick derived field. Still follow clinician instructions for medical clearance.