The short answer: BMI is weight divided by height squared. BMR estimates energy at rest; TDEE estimates daily energy expenditure including activity. All three are estimates or screening tools. They cannot determine a diagnosis, target weight or dietary prescription on their own.
- For adults, consider BMI alongside medical history, blood pressure, tests and body composition.
- BMR and TDEE do not measure an individual’s actual food requirements. They are starting estimates.
- Do not use this page’s general categories for children, adolescents, pregnancy or individual treatment decisions.
What is body mass index (BMI)?
According to the CDC guidance on BMI, body mass index is a simple measure relating weight to height. The adult formula is: weight in kilograms ÷ height in metres squared.
How do I calculate BMI online?
Enter height in centimetres and weight in kilograms in the calculator above. The result appears without creating an account. Age, sex and activity are not needed for BMI; they are used only for optional BMR and daily maintenance-energy estimates.
| BMI | General category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight range |
| 25 to 29.9 | Overweight |
| 30 and above | Obesity |
Limitations of BMI
BMI does not directly measure body fat percentage, fat distribution, muscle, pregnancy or individual differences. A muscular athlete and an older adult may have different body composition at the same BMI. The CDC recommends interpreting individual results alongside medical history, health behaviours, blood pressure, examination and tests such as blood glucose and lipids.
How do BMR and TDEE differ?
Your body uses energy for breathing, pumping blood and brain function even during sleep. Basal metabolic rate, or BMR, estimates energy needs at rest. Multiplying BMR by an activity factor estimates TDEE, an approximate daily energy requirement for maintaining weight.
This tool uses the Mifflin–St Jeor equation for BMR. The activity factor is a general estimate. Actual energy expenditure varies with work, body composition and exercise intensity; wearable estimates also have limits.
How should I use the result?
Treat TDEE as a starting estimate and review weight, energy and performance trends over several weeks. You can also explore the TDEE calculator and macro calculator for context. Our guide to weight-loss plateaus explains why the same calorie number does not always produce the same outcome over time. The guide to resistance training and BMR reviews training effects without promising magical fat burning. Pregnancy, breastfeeding, eating disorders, kidney disease and rapid weight changes require individual professional guidance.
When is a calculator not enough?
Unintentional weight changes, persistent weakness or dizziness, palpitations, swelling, menstrual changes, unusual thirst or urination, and new symptoms after starting medication warrant medical assessment. Adolescents need growth charts specific to age and sex; this adult table is not suitable for interpreting growth.
Sources for the calculations and interpretation
- CDC: BMI and its interpretation limits
- Mifflin and colleagues: resting-energy equation
- Avocado’s scientific source library
Common BMI questions
How do I calculate BMI online?
Enter height in centimetres and weight in kilograms. Avocado divides weight by height in metres squared and shows the result without registration.
Do I need age and sex to calculate BMI?
No. BMI uses only height and weight. Age, sex and activity are used only for optional BMR and daily-energy estimates.
What is the difference between BMI and BMR?
BMI relates weight to height as a general screening measure. BMR estimates energy at rest; its equation also uses age and sex.
Important note
These estimates are intended for adults aged 20 and older. BMI or calculated calories alone cannot establish health status or treatment needs.