If carbs and protein are 4 calories per gram, and fat is 9 calories per gram, why don't my macros' share of calories equal my calorie total for the day?
For calorie counts, we use the manufacturer's nutrition labels for branded foods and U.S. Department of Agriculture (USDA) testing for common foods. We don't arrive at the calorie number based on the common 4:4:9 formula, where carbs and protein equal 4 calories per gram and fat equals 9 calories per gram.
Manufacturers can actually use one of six different methods in calculating calories from macros: the 4:4:9 method, 4:4:9 minus insoluble fiber, Atwater conversion factors, and three other techniques.
The USDA uses Atwater conversion factors, which is a more precise method of calculating calories from macros than the 4:4:9 formula. For more information, see http://nutribase.com/atwater.html.
As a result of these varying methods for deriving calories from macros, the macros you've logged won't exactly match the 4:4:9 formula results.