This couple be a number of reasons. First, make sure you don't over mix the batter. This is probably the number one cause for sunken cupcakes. Secondly, make sure your baking soda and baking powder are still good. u003ca href=u0022https://food52.com/blog/21908-how-can-i-tell-if-baking-powder-is-still-good-to-useu0022 target=u0022_blanku0022 rel=u0022noreferrer noopeneru0022u003eHere is how you test thatu003c/au003e. Cupcakes that don't rise could also be due to an uncalibrated oven (aka the temperature age is not accurate). If you think this is the case, I recommend getting an oven thermometer to place inside to double check.