Calorie Counter

Total calories in food come from adding up each macronutrient's own energy density, a method known as the Atwater system: this calculator applies the standard 4 calories per gram for Protein, 4 for Carbohydrates, 9 for Fat, and 7 for Alcohol — the same general factors the FDA's own Food Labeling Guide cites for the calorie figure on a Nutrition Facts label (21 CFR 101.9(d)(10) for the 9/4/4 protein-carb-fat factors, with alcohol calculated at 21 CFR 101.9(c)(1)(i)(A)'s specific Atwater rate of 7.07 cal/g, rounded to 7 here). Fat is the most calorie-dense macro by a wide margin, so raising Fat always raises Total Calories more per gram than an equal change in Protein or Carbohydrates would. Fiber is handled differently -- it's meant to be entered as the portion of your Carbohydrates figure that's dietary fiber (informational, already counted in the carbs total), and because fiber is only partially digested and fermented rather than fully absorbed, this calculator nets it out at roughly 2 calories per gram instead of the 4 that carbs get credited at, subtracting the difference from Total Calories.

That means raising Fiber (while leaving Carbohydrates unchanged) actually lowers Total Calories, reflecting that not all of a food's carbohydrate content is equally available as usable energy. Protein Calories, Carb Calories, and Fat Calories are each computed independently from their own gram input and don't interact with each other -- Fat is completely inert against Protein Calories, for example, since the two macros are tallied on separate lines before being summed. The macro percentage breakdown (Protein %, Carb %, Fat %, Alcohol %) expresses each macro's calorie contribution as a share of the gross calorie total before the fiber adjustment is applied, so the four percentages always sum to 100% -- Fiber's 2-cal/g netting only affects the Total Calories figure itself, not the percentage breakdown.