Weight Loss Calculator
Accurately plan your weight loss journey. Calculate your daily calorie needs, estimate your timeline, and visualize your progress with our professional-grade financial-style planner.
Imperial (lbs, ft/in)
Metric (kg, cm)
Male
Female
Please enter a valid age (18-100).
Feet and Inches
Centimeters
Must be positive.
Goal must be less than current weight.
Sedentary (Office job, little exercise)
Light Activity (Exercise 1-3 days/week)
Moderate Activity (Exercise 3-5 days/week)
Very Active (Heavy exercise 6-7 days/week)
Extra Active (Physical job + training)
Used to calculate your Total Daily Energy Expenditure (TDEE).
Mild (250 kcal/day) – 0.5 lbs/week
Moderate (500 kcal/day) – 1.0 lb/week
Aggressive (750 kcal/day) – 1.5 lbs/week
Extreme (1000 kcal/day) – 2.0 lbs/week
Standard guidance suggests a 500 kcal deficit for sustainable loss.
Estimated Time to Reach Goal
20 Weeks
Target Date: October 15, 2024
Daily Calories (Intake)
2,050 kcal
To maintain deficit
Maintenance Calories (TDEE)
2,550 kcal
Burned per day
Total Weight to Lose
20 lbs
Projected Weight Loss Trajectory
Weekly Loss Schedule
| Week | Date | Projected Weight | Total Lost |
|---|
What is a Weight Loss Calculator?
A weight loss calculator is a specialized planning tool designed to help individuals determine the mathematical requirements for reaching a specific body weight goal. Unlike generic health tools, this calculator functions similarly to a financial amortization schedule: it treats your current weight as a "principal balance" and your caloric deficit as the "monthly payment" to reduce that balance over time.
This tool is essential for anyone—from athletes cutting for competition to individuals seeking sustainable lifestyle changes—who needs a data-driven approach to weight management. It eliminates the guesswork by providing a concrete timeline based on biological variables like age, gender, height, and activity level.
Common misconceptions often lead people to believe that weight loss is purely about "eating less." However, a proper weight loss calculator accounts for Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE), ensuring that the suggested caloric intake is safe, sustainable, and mathematically sound.
Weight Loss Formula and Mathematical Explanation
To provide precise estimates, this calculator utilizes the Mifflin-St Jeor Equation, widely considered by the dietetic community to be the most accurate standard for calculating metabolic rate.
Step 1: Calculate BMR (Basal Metabolic Rate)
The BMR represents the energy your body burns at complete rest just to maintain vital functions.
- Men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
- Women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Step 2: Calculate TDEE (Total Daily Energy Expenditure)
This adjusts your BMR based on your physical activity level:
- Sedentary: BMR × 1.2
- Moderate Activity: BMR × 1.55
- Very Active: BMR × 1.725
Step 3: The Deficit Calculation
The core principle of weight loss math is the caloric deficit. Scientifically, approximately 3,500 calories of energy deficit equals 1 pound (0.45 kg) of fat loss.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| BMR | Basal Metabolic Rate | kcal/day | 1,200 – 2,200 |
| TDEE | Total Daily Energy Expenditure | kcal/day | 1,500 – 3,500 |
| Deficit | Calories below maintenance | kcal/day | 250 – 1,000 |
Practical Examples
Example 1: The Steady Approach
Scenario: Sarah is a 35-year-old woman, 5'6″ (168cm), weighing 180 lbs (81.6kg). She works an office job (sedentary) but wants to reach 160 lbs.
- BMR Calculation: Approx. 1,550 kcal/day.
- TDEE: 1,550 × 1.2 = 1,860 kcal/day (Maintenance).
- Strategy: She chooses a 500 calorie deficit.
- Daily Target: 1,360 kcal.
- Result: She loses 1 lb per week. It will take her approximately 20 weeks to lose 20 lbs.
Example 2: The Active Approach
Scenario: Mark is a 28-year-old male, 6'0″ (183cm), weighing 220 lbs (100kg). He exercises 5 days a week (Moderate Activity). Goal: 200 lbs.
- TDEE: Approx. 3,100 kcal/day.
- Strategy: He creates a 1,000 calorie deficit.
- Daily Target: 2,100 kcal.
- Result: He loses 2 lbs per week. Time to goal: 10 weeks.
How to Use This Weight Loss Calculator
- Input Your Details: Select your unit system (Metric or Imperial) and enter your current statistics accurately. Honesty here ensures accurate results.
- Set Your Activity Level: Be realistic. Overestimating activity is a common error that leads to slower results. If unsure, choose the lower option.
- Select Desired Deficit:
- Mild (250 kcal): Slow, very sustainable, barely noticeable hunger.
- Moderate (500 kcal): The "Gold Standard." Sustainable with visible results.
- Aggressive (1000 kcal): Difficult to maintain long-term; best for short periods.
- Review the Chart: The line graph visualizes your journey, showing exactly when you will hit milestones.
- Download/Copy: Use the "Copy Results" button to save your caloric targets to your phone or nutrition tracking app.
Key Factors That Affect Results
While the math is precise, biological systems are dynamic. Several factors influence real-world results:
- Metabolic Adaptation: As you lose weight, your body becomes smaller and burns fewer calories. You may need to recalculate your TDEE every 10-15 lbs lost.
- Water Retention: High sodium intake or hormonal fluctuations can cause water weight swings of 2-5 lbs, masking fat loss on the scale.
- Non-Exercise Activity Thermogenesis (NEAT): Subconscious movement like fidgeting often decreases when dieting, lowering your TDEE.
- Sleep Quality: Poor sleep increases hunger hormones (ghrelin) and decreases metabolic efficiency.
- Macronutrient Composition: Protein has a higher thermic effect than fats or carbs, meaning you burn more calories digesting it.
- Stress Levels: Chronic stress elevates cortisol, which can promote water retention and muscle breakdown rather than fat loss.
Frequently Asked Questions (FAQ)
Is it safe to lose more than 2 lbs per week?
Generally, no. Losing more than 1-2 lbs per week (or 1% of body weight) increases the risk of muscle loss, gallstones, and nutritional deficiencies.
Why did my weight loss stop?
You likely hit a plateau because your new, lighter body requires fewer calories. Recalculate your numbers using your current weight to find your new maintenance level.
Should I eat back my exercise calories?
This calculator already accounts for exercise in the "Activity Level" multiplier. Do not add exercise calories on top of this, or you will be "double counting" and erase your deficit.
What is the minimum calorie intake safe for me?
Health organizations generally recommend not dropping below 1,200 kcal for women and 1,500 kcal for men without medical supervision.
Does this calculator work for Ketogenic diets?
Yes. The thermodynamic laws of weight loss (Calories In vs. Calories Out) apply regardless of whether your calories come from carbs or fats.
How accurate is the Mifflin-St Jeor formula?
It is considered the most reliable equation for the general population, typically accurate within +/- 10%.
Can I target fat loss in my belly?
No. "Spot reduction" is a myth. You lose fat systemically; where it comes off first is determined by genetics.
What happens if I eat over my limit one day?
One day won't ruin your progress. Just get back to your plan the next day. Consistency over weeks matters more than perfection in a single day.
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