To calculate net carbs, simply subtract the amount of fiber and sugar alcohols from the total amount of carbohydrates. For example, if a food has 10 grams of carbs, 4 grams of fiber, and 2 grams of sugar alcohols, its net carb count would be 4 grams (10 total carbs - 4 fiber - 2 sugar alcohols = 4 net carbs).