On this page
Which body and fitness tool do you need?
These calculators answer three related questions: how your weight compares with your height, how much energy your body uses, and how many calories you might eat to maintain, lose or gain weight.
- [TDEE calculator](/tdee-calculator) – total daily energy expenditure from the Mifflin-St Jeor equation (or Katch-McArdle if you know your body-fat percentage), with activity multipliers and maintenance, weight-loss and weight-gain targets.
- [BMI calculator](/bmi-calculator) – body mass index in US or metric units, the adult BMI categories, your healthy weight range for your height, and waist-to-height ratio.
- [BMI calculator for men](/bmi-calculator-for-men) – BMI plus waist size and waist-to-height ratio, with the WHO and NICE waist thresholds that matter most for men's health risk.
- [Calorie calculator](/calorie-calculator) – estimated calories per day by age, sex and activity, with gentle and moderate weight-loss targets and the Dietary Guidelines' calorie estimates for comparison.
How the numbers fit together
| Measure | What it estimates | Main inputs |
|---|---|---|
| BMI | Weight relative to height | Weight, height |
| Waist-to-height ratio | Abdominal fat relative to height | Waist, height |
| BMR | Energy used at complete rest | Weight, height, age, sex |
| TDEE | Total energy used per day, including activity | BMR × activity multiplier |
| Calorie target | Intake to maintain, lose or gain weight | TDEE ± an adjustment |
For example, a 40-year-old man who is 178 cm tall and weighs 80 kg has a Mifflin-St Jeor BMR of about 1,718 kcal/day. If he is sedentary, his TDEE is about 2,060 kcal/day; if he is moderately active, about 2,660 kcal/day. His BMI is 25.2, just above the healthy range – which is why the BMI pages also ask for waist size: if his waist-to-height ratio is under 0.5, his weight may well reflect muscle rather than excess fat.
Choosing the right tool
- "Am I a healthy weight?" – start with the BMI calculator, and add a waist measurement.
- "How many calories do I burn?" – the TDEE calculator.
- "How much should I eat to lose weight?" – the calorie calculator, which builds on TDEE and offers rates of loss up to 0.75 kg (1½ lb) a week.
- "I lift weights – is BMI fair to me?" – the BMI calculator for men explains the "athlete problem" and what to check instead.
Limits of these calculators
All of these tools give estimates for adults. Equations such as Mifflin-St Jeor predict the average for people of a given size, age and sex; an individual's true energy use can be several hundred calories higher or lower. BMI does not distinguish muscle from fat and uses lower cut-offs for some ethnic groups. None of these calculators is designed for children, pregnancy or people with eating disorders, and they are not a substitute for advice from a clinician or registered dietitian – especially if you have diabetes, kidney disease or take medicines that affect weight or appetite.
Related tools
- A1C calculator – weight and activity are closely linked to blood sugar.
- Cholesterol calculators – LDL, non-HDL and ratios.
- Due date calculator – for pregnancy, where adult BMI and calorie tools do not apply.
Sources
- Mifflin MD, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990
- Frankenfield D, et al. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc 2005
- CDC – Adult BMI categories
- NICE guideline NG246 – Overweight and obesity management
- US Department of Agriculture and US Department of Health and Human Services. Dietary Guidelines for Americans, 2020–2025