Sunken cupcakes are so frustrating, but typically it happens due to one of the following reasons: Underbaking: When this happens, the cupcakes sink as they cool. Be sure to bake them until a toothpick comes out clean. Overmixing: An excessive amount of air mixed into your batter can cause them to rise quickly and then collapse while baking. Mix just until combined. Too Much Leavening: Carefully measure your baking powder and soda. Opening the Oven Too Soon: Doing so can cause the temperature to rapidly drop. Don't open the oven door to check them until they're at least 75% through their baking time. Incorrect Oven Temperature: An overly hot can set the cupcake's outside before the inside is cooked. An oven thermometer helps ensure accuracy.