BMI Calculator by Age 2026 — Adults & Children

📋 Your Details

Age 2 – 120 years

Biological Sex affects child percentile

Height centimetres

Weight kilograms

⚖️

Fill in your details and hit Calculate to see your age-adjusted BMI, body silhouette, ideal weight, and more.

🧍 Body Silhouette Visualiser

Healthy Range

BMI 18.5–24.9

You

BMI --

🎯 Ideal Weight Range for Your Height

The green zone shows the healthy BMI weight range for your exact height. The circle shows where you are now.

YOU

📊 BMI Percentile for Age (CDC Charts)

For children and teens (ages 2–19), BMI is assessed using age- and sex-specific percentile charts from the CDC. A BMI-for-age percentile below 5th is underweight; 85th–94th is overweight; 95th and above is obese.

📈 Session History

Why BMI Without Age Is Half the Picture

A BMI of 27 means something different at 19 than it does at 65. For adults, the standard cutoffs — underweight below 18.5, normal up to 24.9, overweight up to 29.9, obese at 30 and above — don't account for the fact that body fat percentage naturally shifts as you get older. Muscle mass declines. Fat redistributes. The number on its own doesn't tell the whole story.

For children and teens, raw BMI is almost meaningless without a percentile. A BMI of 20 could be perfectly healthy for a 15-year-old or a red flag depending on their sex and age group. The CDC's BMI-for-age growth charts fix this — and this calculator uses them for anyone under 20.

💡 How this calculator is different

Most BMI calculators just spit out a number and a category. This one gives you an animated gauge, a visual body silhouette, your ideal weight range plotted on a track, age-adjusted interpretation, CDC percentile charts for under-20s, and a session history so you can track changes across multiple measurements.

How to Read Your Results

The Gauge and the Number

The semicircular gauge maps your BMI onto a coloured arc — blue for underweight, green for normal, yellow for overweight, orange for obese class I, red for obese class II+. The needle animates to your exact position. If you're right on the edge between two zones, that's intentional — edges are where the nuance lives.

The Body Silhouette

Your silhouette scales to reflect your BMI category relative to a healthy-range reference. It's a visual anchor, not a medical illustration. Its job is to ground the number in something human-scale — because "27.4" is abstract; seeing proportional difference is not.

The Ideal Weight Track

This shows the full healthy weight range for your exact height — not a single target, but a span. The green fill covers BMI 18.5 to 24.9. Your current weight appears as a circle. If you're inside the green zone, you're done. If you're outside, the tracker shows you how far you'd need to travel in either direction — and the weight cards below give you the specific numbers.

⚠️ For children (ages 2–19)

BMI alone can't classify weight status in children. The percentile chart appears automatically when you enter an age under 20. A reading between the 5th and 85th percentile is considered healthy for that age and sex group — anything outside deserves a conversation with a paediatrician.

Standard BMI Reference — Adults (20+)

Use this as a quick sanity check, not a diagnosis

These are the WHO/CDC adult ranges used by the calculator. Ethnicity adjustments exist — South and East Asian populations may face increased metabolic risk at lower BMI thresholds — but the standard table is the global baseline.

Category	BMI Range	What it generally means
Underweight	Below 18.5	May indicate insufficient nutrition, malabsorption, or other health concerns
Normal weight	18.5 – 24.9	Associated with lowest risk of weight-related chronic disease
Overweight	25.0 – 29.9	Increased risk — but context (muscle mass, fitness level) matters
Obese Class I	30.0 – 34.9	Moderate risk for hypertension, type 2 diabetes, cardiovascular disease
Obese Class II	35.0 – 39.9	High risk — medical guidance strongly recommended
Obese Class III	40.0 and above	Very high risk — consult a healthcare provider

🩺 Important

BMI doesn't measure body fat directly. Athletes, pregnant people, and older adults often get misleading readings. Use this as one data point alongside waist circumference, body fat percentage, and clinical evaluation — not as a standalone verdict.

Frequently Asked Questions

What is a healthy BMI for my age? +

For adults 20 and older, the healthy range is BMI 18.5–24.9 regardless of age — though some researchers argue older adults (65+) fare better toward the higher end of that range (23–27). For children and teens under 20, "healthy" depends on age and sex: the CDC defines healthy as the 5th–85th percentile on age-specific growth charts.

Is BMI accurate for children? +

Not without percentile context. A raw BMI number doesn't tell you much for a 10-year-old. The CDC BMI-for-age charts account for normal changes in body fat as kids grow and the difference between boys and girls at each age. This calculator automatically switches to percentile mode for ages 2–19.

Why is my BMI different from what I calculated before? +

Small input differences add up fast. A height entered as 175 cm vs 174 cm shifts the result by about 0.1 BMI units. Also confirm you're using the right unit system — a common mistake is entering pounds but leaving the calculator set to kilograms. The formula itself is fixed: weight (kg) ÷ height (m)².

What is a good BMI for older adults over 65? +

Some evidence suggests older adults with a BMI between 23 and 27 have better health outcomes than those at the lower end of the standard healthy range. Very low BMI in older adults can indicate muscle loss (sarcopenia) or nutritional issues. The calculator notes this nuance in its interpretation for ages 65+.

How much weight do I need to lose to reach a healthy BMI? +

The ideal weight track in the results shows your exact healthy weight range for your height and the gap between your current weight and the nearest boundary. To hit BMI 24.9 (the upper healthy limit), you'd need to reach: 24.9 × height(m)². The calculator works this out automatically and shows it as a target weight in your stats cards.