Health & Wellbeing2 min check

BMI Calculator

Quick Body Mass Index calculation using the same thresholds the NHS uses for adults aged 18+.

Short answer

BMI = weight (kg) ÷ height (m)². NHS thresholds: under 18.5 = underweight, 18.5–24.9 = healthy, 25–29.9 = overweight, 30+ = obese. South-Asian, Chinese and African-Caribbean adults use lower thresholds (overweight from 23, obese from 27.5).

Step 1 of 10%

Calculation method, coverage and version

Inputs used: Units, Height (cm) — metric, Weight (kg) — metric, Height (ft) — imperial, Height (in) — imperial, Weight (stone) — imperial, Weight (extra lbs) — imperial, Ethnicity (affects threshold).
Calculation approach: The calculator applies the rules and assumptions described in “How it works” to the values you enter. Rounding can cause small differences from an official or provider calculation.
Coverage: Health & Wellbeing. UK nations, tax treatment, local rules and provider criteria can differ; check the official sources shown below before acting.
Content version: No page-specific review date is currently published. Treat the result as indicative and verify current rules independently.

Not included unless explicitly requested: personal circumstances not entered, provider discretion, future rule changes, professional fees and case-specific exceptions. Read the full calculator methodology.

How it works

BMI = weight ÷ height². It's a population-level screening measure. The NHS uses standard thresholds for general adults and lower thresholds for ethnicities at higher cardiometabolic risk at the same BMI (South Asian, Chinese, African-Caribbean).

Worked example

1.75m, 75kg → BMI = 75 ÷ (1.75 × 1.75) = 24.5 → Healthy weight (general thresholds).

Who should use this

•Adults 18+ wanting a quick weight-status indicator
•People starting a weight management plan
•Anyone tracking changes over time

Common mistakes

×Using BMI for very muscular people (over-classifies as overweight)
×Using adult BMI on children (use BMI centile charts instead)
×Forgetting ethnicity-specific thresholds
×Treating BMI as a single source of truth rather than alongside waist size

Frequently asked questions

Is BMI accurate for athletes?▾

Often not — high muscle mass can push BMI into overweight while body fat is low and healthy.

What's a healthy BMI?▾

18.5–24.9 for general adults, 18.5–22.9 for South-Asian, Chinese and African-Caribbean adults.

Should I use BMI for my child?▾

No — children use BMI percentile charts that account for age and sex.

Does BMI predict health risk?▾

Roughly. Waist circumference, blood pressure, cholesterol and HbA1c add much better picture.

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