Carb Calculator

Data Source and Methodology

This calculator provides an estimate of your daily macronutrient needs based on established scientific formulas. All calculations for Basal Metabolic Rate (BMR) are strictly based on the **Mifflin-St Jeor equation**, which is widely regarded as one of the most accurate methods for predicting resting energy expenditure.

• Authoritative Source: Mifflin, M. D., St Jeor, S. T., Hill, L. A., Scott, B. J., Daugherty, S. A., & Koh, Y. O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American journal of clinical nutrition, 51(2), 241–247.
• Reference: https://doi.org/10.1093/ajcn/51.2.241

The Formulas Explained

Your carbohydrate needs are not calculated in isolation. They are part of your total daily energy expenditure (TDEE). Here is the 4-step process:

1. Calculate BMR: First, we find your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor formula.

   Men: $BMR = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) + 5$

   Women: $BMR = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) - 161$

2. Calculate TDEE: Next, we find your Total Daily Energy Expenditure (TDEE) by multiplying your BMR by your chosen activity level.

   $TDEE = BMR \times \text{Activity Factor}$

3. Adjust for Goal: We adjust your TDEE calories based on your goal (e.g., subtracting 500 calories for 1 lb/week weight loss).

   $Goal \text{ Calories} = TDEE + \text{Goal Adjustment}$

4. Calculate Carbs: Finally, we calculate your carbohydrate grams based on a percentage of your Goal Calories. We use the fact that 1 gram of carbohydrate = 4 calories.

   $Carbohydrates \text{ (g)} = \frac{Goal \text{ Calories} \times \% \text{Carbs}}{4}$

Glossary of Variables

• BMR (Basal Metabolic Rate): The number of calories your body needs to function at complete rest (e.g., if you stayed in bed all day).
• TDEE (Total Daily Energy Expenditure): Your BMR plus all the calories you burn from physical activity, digestion, and daily living. This is your "maintenance" calorie level.
• Activity Factor: A multiplier that represents your average daily activity level.
• Goal Adjustment: The number of calories added or subtracted from your TDEE to achieve your goal (e.g., a 500-calorie deficit to lose ~1 lb per week).
• Macronutrients: The three main nutrients that provide energy: Carbohydrates (4 cal/g), Protein (4 cal/g), and Fat (9 cal/g).

How It Works: A Step-by-Step Example

Let's walk through an example for Alex, a 30-year-old male who is 180 cm tall, weighs 80 kg, is "Moderately Active," and wants to "Maintain Weight."

1. Calculate BMR (Male):
   $BMR = (10 \times 80) + (6.25 \times 180) - (5 \times 30) + 5$
   $BMR = 800 + 1125 - 150 + 5 = \textbf{1780 \text{ calories}}$
2. Calculate TDEE:
   The "Moderately Active" factor is 1.55.
   $TDEE = 1780 \times 1.55 = \textbf{2759 \text{ calories}}$
3. Adjust for Goal:
   The "Maintain Weight" goal has a 0-calorie adjustment.
   $Goal \text{ Calories} = 2759 + 0 = \textbf{2759 \text{ calories}}$
4. Calculate Carbs (Balanced Plan):
   The "Balanced" plan allocates 40% of calories to carbs.
   $Carbs \text{ (g)} = (2759 \times 0.40) / 4 = 1103.6 / 4 \approx \textbf{276 \text{ g of carbs}}$

Frequently Asked Questions (FAQ)