Eleven-year-old Alexander (Ed Oxenbould) experiences the most terrible and horrible day of his young life—on the day before his birthday. It begins when he gets gum stuck in his hair. When he arrives at school, photoshopped pictures of him are texted to the entire class body and he accidentally sets a fire in class - in front of a girl he has a crush on. But when Alexander tells his family about his disastrous day, he finds that they're all having nothing but luck and he begins to wonder if bad things only happen to him.

That night, he makes a birthday wish to have his family have their own bad day so they can relate to what he's going through. However, he feels guilty when his brother Anthony (Dylan Minnette), sister (Kerris Dorsey), mom (Jennifer Garner) and dad (Steve Carell) wake up and immediately find themselves living through their own terrible, horrible, no good, very bad day.