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BMI Calculator

Calculate your Body Mass Index using height and weight to assess whether you are underweight, healthy, overweight or obese using standard BMI classifications.

BMI Calculator · AUHealth & Lifestyle
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Results update when you select Calculate.

Example result based on the prefilled values.

BMI

24.50 (Healthy Weight)

Healthy Weight Range

56.70kg - 76.30kg

Waist-to-Height

0.49 (Healthy)

Continue your plan

Useful next calculations

Related to this calculation

When to use this calculator

  • Before setting a new health goal or checking whether a plan is realistic.
  • When you want to compare different assumptions without tracking them manually.
  • When you need a quick baseline before discussing the result with a professional.
  • When you are starting a new fitness or diet programme and want an objective starting-point measurement.
  • When you want to recheck your numbers after several weeks of change to see whether the metrics are moving in the right direction.

A realistic Australia planning example

Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.

Weight (kg)

80 kg

Height (cm)

178 cm

Age

35

Waist Measurement

84 cm

After entering these figures, review bmi, healthy weight range and waist-to-height together rather than in isolation — each metric tells a different part of the story. Then rerun the tool with one input adjusted to see which variable has the biggest effect on all three outputs before you settle on a plan.

How to read your results

BMI

Treat BMI as a broad screening marker rather than a clinical diagnosis, and always read it alongside the other health indicators the tool produces. If the result falls outside the healthy range, discuss it with a GP before making significant changes to diet or exercise.

Healthy Weight Range

This output shows a planning range based on standard BMI thresholds, not a prescriptive personal target, so apply it with context and common sense. Use it as a reference point alongside advice from a healthcare professional rather than as a standalone goal.

Waist-to-Height

Waist measurement adds important context to a headline BMI result and can indicate metabolic risk even when overall weight appears normal. Use it alongside the other outputs to get a more complete picture before drawing any conclusions.

Method & assumptionsAuthoritative sources

Body Mass Index (BMI) is calculated by dividing your weight in kilograms by the square of your height in metres (kg/m²). It was developed in the 19th century as a statistical tool for comparing body size across populations, and it remains one of the most widely used screening metrics in public health. However, BMI was never designed as a diagnostic tool for individuals. It takes no account of age, sex, muscle mass, bone density, or fat distribution — all factors that influence health risk. Use your BMI result as a starting point for a broader conversation about health, not as a definitive verdict. A GP or registered dietitian can provide context based on your full medical history.

Common mistakes

  • !Using an assumption that is not supported by a current local quote, bill, statement or official source.
  • !Treating a generic estimate as a lender, provider, payroll or tax authority decision.
  • !Mixing monthly and annual inputs without converting them consistently.
  • !Forgetting location-specific taxes, fees, eligibility rules or payroll deductions where they apply.
  • !Testing only one scenario instead of checking how a cautious assumption changes the result.

What to do next

  • Run a second scenario with a cautious assumption so you can see the downside clearly.
  • Compare the result with the related calculators below before making a decision.
  • Check current local rules, eligibility and provider terms before applying or committing money.
  • Keep a record of the assumptions so you can update the estimate when a quote, bill or pay figure changes.
  • Use the result to prepare better questions for a lender, provider, adviser or employer rather than treating it as a final answer.

Frequently asked

The NHS and WHO classify BMI as: underweight below 18.5, healthy 18.5-24.9, overweight 25-29.9, obese class 1 30-34.9, obese class 2 35-39.9, and obese class 3 (severely obese) 40+. Lower thresholds apply for people of South Asian, Chinese, Middle Eastern, Black African and African-Caribbean descent (overweight from 23, obese from 27.5) because cardiometabolic risk rises at lower BMI.

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