The Day View Macros pie chart is meant to help those who are conscious of balancing their macronutrient ratios. Which is to say, keeping their intake of calories from protein, fat, and carbohydrates in proportion for the course of a day.
The pie chart will always add up to 100% to show the relative amounts of calories form fat, carbs, and protein you have eaten. It will not reflect how much of a macronutrient you still need to consume to meet your calorie goals: that information can be seen by tapping More or home button then Nutrition in the app or by viewing your diary totals on the website.
As an example, if the only food you logged so far in your day was a tablespoon of butter, your pie chart would show something like 97% fat, 3% protein against a goal of perhaps 30% fat and 15% protein. This is not to say that you have eaten 97% of your fat goal, but rather that of the calories you've consumed, the vast majority of the calories came from fat. Over the course of the day, if you were to log more foods with carbs and protein, the fat ratio percentage would drop, and the other nutrient ratios would increase.
If you upgrade to MyFitnessPal Premium, among other added features is the ability to view a detailed list of foods you've logged that rank highest and lowest in the graph you're viewing. This allows you to quickly determine, for instance, which foods you’re eating are the highest in fat, or the highest in calories, and how frequently you are choosing these items.
The default ratios may also be changed by logging in to our site at http://www.myfitnesspal.com and clicking "Goals" then "Change Goals" and then "Custom". iOS and Android users may change the ratio in the app's Menu (or "More" page) on the "Goals" screen.
Also, please bear in mind that while grams of carbs and protein have 4 calories each, a gram of fat has 9 calories. So fewer grams of fat will gain purchase on the pie chart faster than grams of carbs or protein. The Nutrition page in the app shows your current intake in GRAMS of fat, carbs and protein, but the pie chart is showing the ratio of CALORIES.