Weight Loss Calculator: How Much Should You Eat to Lose Weight Fast

Lisa is 34 years old, weighs 82 kg, and wants to reach 70 kg before summer. She exercises a few times a week but struggles to figure out how many calories she should eat to lose weight safely and effectively.

She has tried guessing calories before, sometimes eating too little and losing energy, or too much and seeing no results. Lisa needs a clear plan that fits her body, activity, and goals.

This is exactly why a Weight Loss Calculator is useful — it turns confusion into a simple, personalized daily calorie target.

What Is a Weight Loss Calculator?

A Weight Loss Calculator is a tool that estimates:

• How many calories you should eat per day to reach your target weight.
  
• How much weight you can safely lose per week.
  
• How long it will take to reach your goal.
  

It takes into account your age, gender, height, current and target weight, activity level, and chosen weight loss speed.

Instead of guessing, you get a scientifically-backed, personalized plan.

Why Is This Important?

1. Prevents extreme dieting: Avoid under-eating that can slow metabolism.
   
2. Keeps energy stable: Proper calories help maintain energy for work and exercise.
   
3. Supports healthy weight loss: Safe weight loss is usually 0.5–1 kg per week.
   
4. Tracks progress: You know how long it will take to reach your goal.
   
5. Customizes your plan: Everyone’s body is different — this is tailored for you.
   

Formula Behind the Calculator

The calculator uses well-established formulas:

1. Calculate Maintenance Calories (TDEE)
   

TDEE = BMR × Activity Factor

Where:

• BMR (Basal Metabolic Rate) = Calories your body burns at rest
  
• Activity Factor = Sedentary, lightly active, moderately active, very active, extremely active
  

Example (Mifflin-St Jeor Formula for women):

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

2. Calculate Daily Calorie Deficit
   

Calorie Deficit = Calories to Eat per Day – Maintenance Calories

• Typical safe deficit = 500–1000 calories/day → ~0.5–1 kg weight loss per week
  

3. Estimate Weight Loss & Time
   

Projected Weight Loss (kg/week) = Calorie Deficit ÷ 7700

Time to Reach Goal (weeks) = (Current Weight – Target Weight) ÷ Projected Weight Loss

Note: 1 kg of body fat ≈ 7700 calories

How the Calculator Works – Step by Step

1. Enter your personal information: Gender, age, height, current weight, and target weight.
   
2. Select activity level:
   
   • Sedentary (little or no exercise)
     
   • Lightly active (1–3 days/week)
     
   • Moderately active (3–5 days/week)
     
   • Very active (6–7 days/week)
     
   • Extremely active (heavy physical job + training)
     
3. Choose weight loss speed: Slow, moderate, or fast.
   
4. Press calculate:
   
   • See your daily calorie target.
     
   • See projected weekly weight loss.
     
   • See time to reach goal.
     

See calorie deficit and maintenance calories.