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Weight Loss Equations Calculator

BMI equals weight in kg divided by height in meters squared

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Body Mass Index (BMI)

BMI screens body fat from height and weight. A BMI of 18.5–24.9 is normal, 25–29.9 overweight, and 30+ obese. It does not distinguish muscle from fat.

BMI = weight_kg / height_m²

Basal Metabolic Rate (BMR)

The Harris-Benedict equation estimates calories burned at rest based on weight, height, and age. Female and male versions use different coefficients.

BMR = 66 + 13.7w + 5h − 6.8a (male)

How It Works

This calculator bundles five weight-management equations. BMI screens body fat from height and weight. The Harris-Benedict BMR equations estimate calories burned at rest. Body fat percentage compares lean mass to total weight. TDEE multiplies your BMR by an activity factor to estimate total daily calorie needs.

Example Problem

A 30-year-old male weighs 80 kg and is 180 cm tall. What is his BMI and BMR?

  1. BMI = 80 / (1.80)² = 24.7 (normal range)
  2. BMR (male) = 66 + (13.7 × 80) + (5 × 180) − (6.8 × 30) = 1,858 cal/day
  3. TDEE at moderate activity (1.55×): 1,858 × 1.55 ≈ 2,880 cal/day

Key Concepts

BMI provides a quick population-level screen for body fat but cannot distinguish muscle from fat. The Harris-Benedict BMR equations estimate resting energy expenditure from weight, height, age, and sex. TDEE multiplies BMR by an activity factor to approximate total daily calorie needs, forming the basis for weight management planning.

Applications

  • Clinical nutrition: establishing calorie targets for hospital patients and post-surgical recovery plans
  • Weight management: calculating calorie deficits for safe, sustainable fat loss at 0.5-1 kg per week
  • Sports nutrition: estimating energy requirements for athletes in training and competition phases
  • Public health screening: using BMI to identify overweight and obesity trends in population studies

Common Mistakes

  • Treating BMI as a definitive measure of health — muscular athletes often have high BMIs without excess body fat
  • Using the wrong BMR equation for sex — male and female Harris-Benedict coefficients differ significantly, and swapping them gives errors of 100-200 calories per day
  • Overestimating activity level when calculating TDEE — most sedentary office workers should use a factor of 1.2, not 1.55
  • Creating extreme calorie deficits — eating more than 1,000 calories below TDEE risks muscle loss, nutrient deficiency, and metabolic adaptation

Frequently Asked Questions

What is a healthy BMI range?

A BMI of 18.5–24.9 is considered normal weight. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classified as obese. BMI does not distinguish between muscle and fat, so athletes may score higher without excess fat.

How many calories should I eat to lose weight?

A common guideline is to eat 500 fewer calories per day than your TDEE, which produces about 1 pound of fat loss per week (3,500 calories = 1 lb). Losing more than 2 lbs per week is generally not recommended without medical supervision.

What is the difference between BMR and TDEE?

BMR is the calories your body burns at complete rest (just to keep organs functioning). TDEE adds the calories burned through daily activity and exercise. TDEE is always higher than BMR.

What is a healthy body fat percentage?

For men, 10–20% body fat is considered fit; for women, 18–28%. Essential fat minimums are roughly 3–5% for men and 10–13% for women. These ranges vary by age and fitness level.

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