Weight Loss Calculator

Estimate your BMI, basal metabolic rate (BMR), total daily energy expenditure (TDEE), optimal calorie intake for weight loss, and realistic timeline to reach your target weight. Built on validated formulas (Mifflin-St Jeor, WHO BMI classification) and physical activity guidelines.

?‍⚕️ Female 165cm / 70kg / 30y / Moderate ?‍⚕️ Male 180cm / 85kg / 35y / Active ?️ Athlete 175cm / 75kg / 28y / Very active ? Senior female 160cm / 68kg / 60y / Light
Privacy first: All calculations are performed locally in your browser. No personal data is stored or transmitted.
Disclaimer: This tool provides informational estimates only. It does not replace professional medical advice. Always consult a registered dietitian or physician before starting any weight loss or diet plan.

Understanding the Science of Weight Loss

Effective and sustainable weight loss relies on a consistent calorie deficit — consuming fewer calories than your body burns. Our calculator uses the Mifflin-St Jeor equation, considered the most accurate BMR predictor for general populations (validated by the ADA). Your TDEE is BMR multiplied by activity level, providing a personalized maintenance calorie baseline.

? Mifflin-St Jeor Equation:

Male: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age) + 5

Female: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age) – 161

* Results are in kcal/day. Activity multipliers range from 1.2 (sedentary) to 1.9 (elite athlete).

Why a Moderate Deficit Works Best

Crash diets often lead to muscle loss, metabolic adaptation, and weight regain. Our planner targets a deficit of ~500 calories per day, which yields about 0.5 kg (1 lb) of fat loss per week — a rate recommended by the CDC, WHO, and major health organizations. This gradual method preserves lean mass and supports long-term adherence.

BMI Classification (WHO Standard)

  • Underweight: < 18.5
  • Normal weight: 18.5 – 24.9
  • Overweight: 25 – 29.9
  • Obesity class I/II/III: ≥ 30

Research shows that maintaining a BMI within the normal range reduces risk for cardiovascular disease, type 2 diabetes, and certain cancers. However, individual body composition and muscle mass should also be considered.

Critical Factors for Successful Weight Management

Strength training: Preserves muscle mass during calorie deficit.
Protein intake: 1.6–2.2 g/kg body weight enhances satiety and muscle retention.
Sleep & stress: Poor sleep elevates cortisol, which hinders fat loss.
NEAT (Non-Exercise Activity): Walking, stairs, and daily movement significantly boost TDEE.
Case Study: Sarah’s Sustainable Transformation

Sarah, 34, 168 cm, 78 kg, moderately active (TDEE ~2250 kcal). She used our calculator to set a goal of 66 kg with a deficit of 500 kcal/day (intake ~1750 kcal). Over 24 weeks she lost 12 kg, combining calorie tracking with walking 8k steps/day. The timeline matched the calculator estimate. Her doctor confirmed improved blood markers. This evidence-based approach reduced emotional eating and supported metabolic health.

Frequently Asked Questions

The Mifflin-St Jeor equation has ~90% accuracy for most individuals. However, metabolic differences may vary by ±200 kcal. Adjust based on real-world results: if weight loss stalls for 2+ weeks, reduce intake by 100-150 kcal or increase activity.

The calculator warns if your target BMI falls below 18.5. We recommend a realistic minimum goal inside the healthy BMI range. Extreme deficits can cause nutritional deficiencies and muscle wasting.

Not mandatory, but tracking protein and fiber helps manage hunger. The macro split we provide (30% protein, 30% fat, 40% carbs) is a balanced starting point for most active individuals.

Yes, but athletes may require higher protein and calorie adjustments based on training intensity. The “super active” multiplier (1.9) is designed for endurance athletes or heavy physical labor.
Scientific references: Mifflin MD et al. (1990) – "A new predictive equation for resting energy expenditure"; WHO Expert Consultation (2004) "BMI classification"; CDC Healthy Weight Guidelines. Tool last updated: June 2026.