About

Carbohydrate miscalculation is the primary reason most diet plans fail within the first month. Consuming too few carbs leads to muscle glycogen depletion, cognitive fog, and training performance drops of 15 - 30%. Excess intake drives lipogenesis and insulin resistance over time. This calculator determines your daily carbohydrate requirement by first computing your Basal Metabolic Rate via the Mifflin-St Jeor equation, scaling it by a validated activity multiplier to produce Total Daily Energy Expenditure (TDEE), then applying your selected macronutrient ratio. The result is expressed in both kcal and g using the Atwater factor of 4 kcal/g for carbohydrates. It assumes standard thermic effect values and does not account for metabolic adaptation beyond week 4 of a caloric deficit.

Pro tip: if you train fasted, shift 40% of your daily carb allocation to the post-workout meal to replenish glycogen stores. For individuals with insulin resistance or PCOS, the Low-Carb or Keto presets are more appropriate starting points than the balanced split. Note that fiber, a carbohydrate subtype, is not fully digested and contributes roughly 2 kcal/g rather than 4. This tool does not distinguish net carbs from total carbs.

Formulas

Daily carbohydrate intake is derived from Total Daily Energy Expenditure. First, Basal Metabolic Rate is computed using the Mifflin-St Jeor equation.

For males:

BMR = 10 × W + 6.25 × H − 5 × A + 5

For females:

BMR = 10 × W + 6.25 × H − 5 × A − 161

Where W = body weight in kg, H = height in cm, A = age in years.

TDEE = BMR × AF

Where AF = Activity Factor ranging from 1.2 (sedentary) to 1.9 (extra active). Adjusted calories incorporate the goal modifier:

Calories_adj = TDEE + Goal_offset

Where Goal_offset ranges from −500 kcal (fat loss) to +500 kcal (muscle gain). Daily carbohydrate grams are then:

Carbs = Calories_adj × Carb_%4

The denominator 4 is the Atwater general factor: 1 g of carbohydrate yields approximately 4 kcal of metabolizable energy.

Reference Data

Food (per 100g)	Total Carbs (g)	Fiber (g)	Sugar (g)	Glycemic Index	Category
White Rice (cooked)	28.2	0.4	0.1	73	Grain
Brown Rice (cooked)	23.5	1.8	0.4	68	Grain
Oats (dry)	66.3	10.6	0.0	55	Grain
Quinoa (cooked)	21.3	2.8	0.9	53	Grain
Sweet Potato (baked)	20.1	3.3	6.5	63	Tuber
White Potato (boiled)	17.0	1.8	0.8	78	Tuber
Banana	22.8	2.6	12.2	51	Fruit
Apple	13.8	2.4	10.4	36	Fruit
Blueberries	14.5	2.4	10.0	53	Fruit
Orange	11.8	2.4	9.4	43	Fruit
Whole Wheat Bread	43.3	6.8	5.6	69	Bread
White Bread	49.0	2.7	5.0	75	Bread
Pasta (cooked)	25.0	1.8	0.6	49	Pasta
Lentils (cooked)	20.1	7.9	1.8	32	Legume
Chickpeas (cooked)	27.4	7.6	4.8	28	Legume
Black Beans (cooked)	23.7	8.7	0.3	30	Legume
Corn (boiled)	18.7	2.0	3.2	52	Vegetable
Broccoli	7.0	2.6	1.7	10	Vegetable
Carrots	9.6	2.8	4.7	39	Vegetable
Spinach	3.6	2.2	0.4	15	Vegetable
Milk (whole)	4.8	0.0	5.1	27	Dairy
Greek Yogurt	3.6	0.0	3.2	11	Dairy
Honey	82.4	0.2	82.1	58	Sweetener
Table Sugar	100.0	0.0	100.0	65	Sweetener
Dark Chocolate (70%)	46.0	11.0	24.0	23	Snack
Almonds	21.6	12.5	4.4	0	Nut
Peanut Butter	20.0	6.0	9.0	14	Nut
Watermelon	7.6	0.4	6.2	76	Fruit
Mango	15.0	1.6	13.7	56	Fruit
Couscous (cooked)	23.2	1.4	0.1	65	Grain

Frequently Asked Questions

Activity factor multiplies your BMR to produce TDEE. A sedentary individual (AF = 1.2) with a BMR of 1600 kcal has a TDEE of 1920 kcal. The same person at very active (AF = 1.725) reaches 2760 kcal. At a 50% carb split, that is the difference between 240 g and 345 g of carbs per day. If you train with weights 4+ days/week AND do cardio, select "Very Active" rather than "Moderately Active".

Below approximately 50 g/day, the body depletes liver glycogen within 24-48 hours and shifts to ketogenesis, producing ketone bodies (beta-hydroxybutyrate, acetoacetate) as alternative brain fuel. This is the physiological basis of ketogenic diets. Performance in high-intensity anaerobic exercise (sprints, heavy lifts) typically declines because the phosphocreatine and glycolytic systems depend on glucose. Endurance at moderate intensity may be preserved after a 2-4 week adaptation period.

The original Harris-Benedict equation (1919) was derived from a population sample that is no longer representative of modern body compositions. Mifflin-St Jeor (1990) was validated against indirect calorimetry in a more diverse population and has a standard error of approximately ±10%, compared to ±14% for Harris-Benedict. The American Dietetic Association recommends Mifflin-St Jeor as the most accurate predictive equation for non-obese individuals.

For general health, even distribution across 3-5 meals prevents large glycemic spikes. For athletes, front-loading 30 - 40% of daily carbs in the pre- and post-workout window (within 2 hours) optimizes glycogen resynthesis. The rate of glycogen replenishment peaks at approximately 1.0 - 1.2 g/kg/hr when combining glucose with a small amount of protein. This calculator provides a meal breakdown to help you plan this distribution.

Body fat percentage is not directly used in the Mifflin-St Jeor equation. However, for individuals with high body fat (>30%), the equation may overestimate BMR because adipose tissue is metabolically less active than lean mass. In such cases, using an adjusted body weight or the Katch-McArdle formula (which requires lean body mass) can be more accurate. This tool uses Mifflin-St Jeor as the standard but the results should be treated as an estimate for obese individuals.

Total carbohydrates include all digestible sugars, starches, and fiber. Net carbs subtract fiber and certain sugar alcohols because they are not fully absorbed. Fiber yields roughly 2 kcal/g via colonic fermentation rather than the standard 4 kcal/g. This calculator reports total carbs. If you follow a keto protocol tracking net carbs, subtract your daily fiber intake (typically 25 - 35 g) from the result.