Why are my cakes sinking in the middle or not rising as high as yours?

This could be the result of a few things: your baking powder and/or baking soda is expired (I don’t use anything older than 6 months from the time I buy it); you may be over-mixing your batter (when you add the dry ingredients to the wet ingredients, make sure your mixer is on low and that you mix only until the dry ingredients are incorporated; or your internal oven temperature is off from what the screen is telling you (also make sure you give your oven 20 to 30 minutes to preheat).