BMI Calculator: Chart, Formula & Healthy Range [2026]

Answer first: BMI = weight(kg) ÷ height(m)² — or 703 × lb ÷ in² in imperial units. A healthy adult BMI is 18.5–24.9. Example: 70kg at 1.75m → 70 ÷ 3.0625 = 22.9. Check yours in seconds with the free BMI calculator, which also shows your healthy weight range.

The WHO BMI chart

BMI	Category	What it signals
Below 18.5	Underweight	Possible nutrient deficiency; investigate cause
18.5 – 24.9	Healthy	Lowest population risk zone
25.0 – 29.9	Overweight	Risk rising; lifestyle change usually enough
30.0 – 34.9	Obesity class I	Clinical follow-up advised
35.0 – 39.9	Obesity class II	Higher comorbidity risk
40+	Obesity class III	Specialist care recommended

Worked examples (both unit systems)

Metric: 85kg, 1.80m → 85 ÷ 3.24 = 26.2 (overweight; healthy range for 1.80m is ~60–81kg).
Imperial: 150lb, 65in → 703 × 150 ÷ 4225 = 25.0 (borderline; small changes move the category).
Target weight: for 1.70m, healthy = 18.5×2.89 to 24.9×2.89 ≈ 53.5–72kg.

When BMI lies: muscle, age, and build

BMI is a screening tool, not a diagnosis. It overstates fat in lifters, athletes, and broad-framed people, and understates risk in "skinny-fat" cases with low muscle and belly fat. Always cross-check with waist circumference (under half your height is the popular target) and trends over months, not single readings. Pair the BMI check with the calorie/TDEE calculator to turn the number into a daily plan.

Moving your BMI safely

Find your target range with the BMI calculator (it shows the exact kg/lb band for your height).
Get your maintenance calories from the TDEE calculator.
Aim ~500kcal/day deficit (or surplus if underweight) — roughly 0.5kg per week.
Lift 2–3x weekly with high protein (~1.6–2.2g/kg) so lost weight is fat, not muscle.
Re-check monthly; waist and strength trends matter more than weekly noise.

Common BMI mistakes

Wrong units: cm instead of m in the formula inflates BMI 10,000x — use the calculator to avoid unit errors.
One reading, big conclusions: hydration, meals, and time of day shift weight 1–2kg; track the 4-week trend.
Kids on adult cutoffs: children and teens need age-and-sex percentiles — adult bands do not apply.
Chasing 22.0 exactly: anywhere inside 18.5–24.9 with a healthy waist is a win; the middle is not magic.

Conclusion

BMI takes ten seconds and points the right direction — then waist, habits, and trends finish the story. Start with the free BMI calculator and build your plan from there.

Frequently Asked Questions

How is BMI calculated?

Metric: weight(kg) ÷ height(m)². Imperial: 703 × weight(lb) ÷ height(in)². Example: 70kg at 1.75m → 70 ÷ 3.0625 = 22.9, solidly in the healthy range.

What is a healthy BMI?

WHO defines 18.5–24.9 as healthy for adults, under 18.5 underweight, 25–29.9 overweight, and 30+ obese (with classes I–III at 30, 35, and 40).

Is BMI accurate for muscular people?

Not really — BMI cannot tell muscle from fat, so lifters and athletes often score "overweight" while lean. Pair it with waist circumference or body-fat estimates for the full picture.

Does healthy BMI differ by age?

The adult cutoffs stay the same, but interpretation shifts: older adults may be healthiest near the upper-middle of the range, while children and teens use age-and-sex percentiles, not adult cutoffs.

What waist size should accompany a healthy BMI?

As a rule of thumb, keep waist under half your height, and generally below 40in (men) / 35in (women) for lower cardiometabolic risk — even with a normal BMI.

How fast should I aim to change BMI?

About 0.5–1% of body weight per week (≈0.5–1kg for most adults). A 500kcal daily deficit with protein and strength training preserves muscle while the number moves.