Weight Loss Calculator
Scientifically calculate how to lose weight by determining your optimal calorie deficit, BMR, and projection timeline.
Metric (kg, cm)
Imperial (lbs, ft/in)
Female
Male
Required for metabolic rate formula.
Please enter a valid age (15-100).
Sedentary (Little or no exercise)
Lightly Active (Exercise 1-3 days/week)
Moderately Active (Exercise 3-5 days/week)
Very Active (Exercise 6-7 days/week)
Extra Active (Very physical job/training)
Affects your Total Daily Energy Expenditure (TDEE).
Mild (0.25 kg / 0.5 lb per week)
Normal (0.5 kg / 1 lb per week)
Aggressive (0.75 kg / 1.5 lb per week)
Very Aggressive (1 kg / 2 lb per week)
Aggressive goals require lower calorie intake.
Daily Calorie Target
2,050 kcal
Eat this amount daily to reach your goal.
Estimated Time
20 Weeks
Maintenance Calories (TDEE)
2,550 kcal
Basal Metabolic Rate (BMR)
1,750 kcal
Projected Weight Loss Trajectory
Monthly Progress Schedule
| Month | Projected Weight | Total Loss | Status |
|---|
What is the Best Way to Calculate How To Lose Weight?
When you set out to calculate how to lose weight, you are essentially solving a biological energy equation. Weight loss occurs when your energy expenditure (calories burned) exceeds your energy intake (calories consumed). This is known as a caloric deficit.
While the concept is simple, the calculation requires precision. It is not just about eating less; it is about finding the specific number of calories that allows your body to burn fat while preserving muscle mass and maintaining metabolic health. This calculator uses the industry-standard Mifflin-St Jeor equation to estimate your needs based on your unique body composition.
Anyone looking to manage their health—from athletes cutting for competition to individuals seeking long-term lifestyle changes—should use a structured method to calculate how to lose weight rather than guessing. Miscalculations can lead to "yo-yo dieting" or metabolic slowdown.
Formula and Mathematical Explanation
To accurately calculate how to lose weight, we must first determine your baseline energy needs. The process involves three distinct steps:
- Calculate BMR (Basal Metabolic Rate): The energy your body needs just to exist at rest (breathing, circulating blood).
- Calculate TDEE (Total Daily Energy Expenditure): Your BMR multiplied by an activity factor. This is your "maintenance" level.
- Apply Deficit: Subtracting calories to create weight loss.
The Mifflin-St Jeor Equation
This is considered the most accurate formula for the general population:
- Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Variable Definitions
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| BMR | Basal Metabolic Rate | kcal/day | 1200 – 2200 |
| TDEE | Total Daily Energy Expenditure | kcal/day | 1500 – 3500 |
| Deficit | Calories removed from TDEE | kcal/day | 250 – 1000 |
Note: 1 kg of body fat contains approximately 7,700 kcal of energy. To lose 0.5 kg (approx 1 lb) per week, you need a deficit of roughly 550 kcal per day (3,850 kcal per week).
Practical Examples
Example 1: Moderate Weight Loss
Scenario: Sarah is a 35-year-old female, 165 cm tall, weighing 80 kg. She works an office job (Sedentary) and wants to calculate how to lose weight safely.
- BMR Calculation: (10 × 80) + (6.25 × 165) – (5 × 35) – 161 = 1,495 kcal/day.
- TDEE Calculation: 1,495 × 1.2 (Sedentary) = 1,794 kcal/day.
- Goal: Lose 0.5 kg per week (requires ~550 kcal deficit).
- Target Intake: 1,794 – 550 = 1,244 kcal/day.
Interpretation: Sarah needs to eat approximately 1,244 calories daily to reach her goal in steady increments without starvation.
Example 2: Active Male
Scenario: Mark is a 28-year-old male, 180 cm tall, weighing 95 kg. He goes to the gym 4 times a week (Moderately Active).
- BMR Calculation: (10 × 95) + (6.25 × 180) – (5 × 28) + 5 = 1,940 kcal/day.
- TDEE Calculation: 1,940 × 1.55 (Moderate) = 3,007 kcal/day.
- Goal: Aggressive cut of 1 kg per week (requires ~1,100 kcal deficit).
- Target Intake: 3,007 – 1,100 = 1,907 kcal/day.
Interpretation: Even though Mark is dieting aggressively, his high activity level means he can still eat nearly 2,000 calories while losing weight rapidly.
How to Use This Calculator
Follow these steps to effectively calculate how to lose weight:
- Select Your Units: Choose Metric (kg/cm) or Imperial (lbs/ft).
- Enter Personal Data: Input accurate age, gender, height, and current weight.
- Assess Activity Honestly: Be realistic. If you sit at a desk all day and walk the dog for 20 minutes, choose "Sedentary" or "Lightly Active". Overestimating activity is a common error.
- Choose Pace: Select how fast you want to lose weight. Faster is not always better; a deficit larger than 1,000 calories is generally not recommended without medical supervision.
- Review Results: The tool will display your daily calorie budget. Stick to this number consistently.
Key Factors That Affect Weight Loss Results
When you calculate how to lose weight, mathematical formulas provide a baseline, but biological factors introduce variables:
- Metabolic Adaptation: As you lose weight, your body becomes smaller and more efficient, meaning your BMR drops. You may need to recalculate your numbers every 5-10 kg lost.
- TEF (Thermic Effect of Food): Protein requires more energy to digest than fats or carbs. A high-protein diet can effectively increase your TDEE slightly.
- Non-Exercise Activity (NEAT): Fidgeting, standing, and walking affect your burn rate. Two people with the same "Sedentary" job might burn different amounts based on NEAT.
- Sleep & Stress: Cortisol (stress hormone) and lack of sleep can lead to water retention and muscle loss, masking fat loss progress on the scale.
- Sodium Intake: High salt intake causes water retention, which can make it look like you aren't losing weight even if you are in a deficit.
- Accuracy of Tracking: The biggest factor is human error. Underestimating food intake by 200 calories a day can halt progress for weeks.
Frequently Asked Questions (FAQ)
How accurate is this calculator?
The Mifflin-St Jeor equation is accurate to within 10% for most people. However, individual metabolism varies. Use the result as a starting point and adjust after 2-3 weeks based on real-world progress.
Can I target fat loss in my belly?
No. When you calculate how to lose weight, you create a systemic energy deficit. Your body decides where to mobilize fat from based on genetics. You cannot spot-reduce fat.
Should I eat back my exercise calories?
Generally, no. If you set your activity level correctly in the calculator (e.g., "Moderately Active"), your exercise calories are already accounted for in the TDEE. Adding them again would be "double dipping" and stop weight loss.
Is it safe to lose weight fast?
Losing more than 1% of your body weight per week is usually considered risky. It increases the chance of muscle loss, gallstones, and nutritional deficiencies.
Why did my weight loss stop?
This is a plateau. It usually happens because you have lost weight, so your BMR has dropped, and you are no longer in a deficit. Recalculate your numbers with your new lower weight.
Does meal timing matter?
For weight loss mechanics, total daily calories matter more than timing. However, intermittent fasting or specific timing might help with adherence and hunger control.
What if the calorie result seems too high?
Many people chronically under-eat and damage their metabolism. If the number seems high, try it for two weeks. You might be surprised that you can lose weight on higher calories if your activity supports it.
How do I track my intake?
Use digital food scales and tracking apps. Estimating portion sizes by eye is the number one reason people fail to match the results when they calculate how to lose weight.
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