Built With Science Calorie & Macro Calculator
Use this calculator to estimate your daily calorie needs and macronutrient breakdown, based on principles often discussed in the "Built With Science" methodology. This provides a science-backed starting point for your fat loss, muscle gain, or maintenance journey.
Sedentary (little to no exercise)
Lightly Active (light exercise/sports 1-3 days/week)
Moderately Active (moderate exercise/sports 3-5 days/week)
Very Active (hard exercise/sports 6-7 days/week)
Extremely Active (very hard exercise/physical job)
Maintenance
Fat Loss
Muscle Gain
Understanding Your Calorie and Macronutrient Needs
Achieving your fitness goals, whether it's fat loss, muscle gain, or maintaining your current physique, hinges significantly on understanding and managing your daily calorie intake and macronutrient distribution. The "Built With Science" approach emphasizes a data-driven strategy, starting with an accurate estimation of these numbers.
How the Calculator Works
This calculator uses the widely accepted Mifflin-St Jeor equation to estimate your Basal Metabolic Rate (BMR), which is the number of calories your body burns at rest. It then factors in your activity level to determine your Total Daily Energy Expenditure (TDEE), representing the total calories you burn in a day.
- BMR (Basal Metabolic Rate): The energy expended while at rest in a neutrally temperate environment, in the post-absorptive state (meaning the digestive system is inactive, which requires about 12 hours of fasting). It's the minimum amount of energy required to keep you alive.
- TDEE (Total Daily Energy Expenditure): Your BMR multiplied by an activity factor. This accounts for the calories burned through exercise, daily movement, and the thermic effect of food.
Adjusting for Your Goal
Once your TDEE is established, the calculator adjusts your calorie intake based on your chosen goal:
- Fat Loss: A moderate calorie deficit (typically 300-500 calories below TDEE) is applied to encourage your body to use stored fat for energy. This deficit is crucial for sustainable fat loss without excessive muscle loss.
- Muscle Gain: A slight calorie surplus (typically 200-400 calories above TDEE) provides the necessary energy and building blocks for muscle growth. Too large a surplus can lead to unnecessary fat gain.
- Maintenance: Your TDEE is used as your target calorie intake to maintain your current body weight.
Macronutrient Breakdown
Beyond total calories, the distribution of macronutrients (protein, fats, and carbohydrates) is vital for body composition. The calculator provides a breakdown based on common "Built With Science" recommendations:
- Protein: Essential for muscle repair and growth, satiety, and has a higher thermic effect than other macros. Recommendations typically range from 0.8 to 1.0 grams per pound of body weight (or 1.8-2.2g per kg) for active individuals, especially during fat loss or muscle gain phases. This calculator uses 1g/lb (2.2g/kg) as a robust target.
- Fats: Crucial for hormone production, nutrient absorption, and overall health. A moderate intake (typically 20-30% of total calories) is recommended. This calculator targets 25% of your total calories from fat.
- Carbohydrates: Your body's primary energy source, fueling workouts and daily activities. The remaining calories after protein and fat are allocated to carbohydrates.
Example Calculation:
Let's consider a 30-year-old male, 180 lbs (81.6 kg), 70 inches (177.8 cm) tall, moderately active, aiming for fat loss:
- BMR Calculation (Mifflin-St Jeor for Men):
BMR = (10 * 81.6 kg) + (6.25 * 177.8 cm) – (5 * 30 years) + 5
BMR = 816 + 1111.25 – 150 + 5 = 1782.25 calories - TDEE Calculation (Moderately Active):
TDEE = BMR * 1.55 (activity factor)
TDEE = 1782.25 * 1.55 = 2762.4 calories - Target Calories (Fat Loss):
Target Calories = TDEE – 400 (moderate deficit)
Target Calories = 2762.4 – 400 = 2362.4 calories (approx. 2362) - Macronutrient Breakdown (based on 2362 calories):
- Protein: 1g/lb body weight = 180g protein
Protein Calories = 180g * 4 cal/g = 720 calories - Fats: 25% of Target Calories = 0.25 * 2362 = 590.5 calories
Fat Grams = 590.5 calories / 9 cal/g = 65.6g (approx. 66g) - Carbohydrates: Remaining Calories = 2362 – 720 – 590.5 = 1051.5 calories
Carb Grams = 1051.5 calories / 4 cal/g = 262.9g (approx. 263g)
- Protein: 1g/lb body weight = 180g protein
This example demonstrates how the calculator arrives at the recommended calorie and macro targets, providing a solid foundation for your nutrition plan.
Important Considerations
These numbers are estimates and a starting point. Individual metabolism, training intensity, and adherence can vary. It's recommended to track your progress (weight, measurements, strength) and adjust your intake every few weeks based on how your body responds. Consistency and patience are key to long-term success.