One large egg contains roughly 72 calories. However, most of an egg's calories are in the egg yolk. One large egg white contains only 17 calories compared to the yolk, which contains 55.
Although the yolk contains the bulk of an egg's fat and calories, it also contains many of the egg's nutrients. One large egg yolk contains more than 40 percent of the total protein of an egg. Almost all of the vitamins A, B6, B12, D and E are contained in the yolk, as well as the calcium, zinc and iron. If making scrambled eggs or other egg-based dishes, consider using at least one yolk for every two or three egg whites so you get more of the egg's nutritional benefits.