The film begins with Cal Weaver, (Steve Carell) a middle-aged man, being told by his wife Emily (Julianne Moore) – to whom he has been married for almost 25 years – that she has cheated on him with a coworker, David Lindhagen (Kevin Bacon), and wants a divorce. On the way home from dinner, Cal refuses to speak to Emily while she drives and tries to verbalize where their marriage went wrong and what led her to cheat. Cal requests that Emily stop talking but she continues, Cal opens the passenger door and rolls out of the moving car. Cal and Emily arrive home where 17-year-old Jessica Riley (Analeigh Tipton) is babysitting their middle-school-aged son (who is in love with Jessica) and youngest daughter. Jessica notices how beat up and dirty Cal looks (from having jumped out of the car) and asks what happened. Cal tells the truth about Mrs. Weaver wanting a divorce not realizing that his son Robbie (Jonah Bobo) is standing in the living room. Embarrassed and ashamed that Robbie had to find out that way, Cal offers to drive Jessica home. As Cal drops Jessica off she tries to cheer him up saying how Mrs. Weaver is crazy for wanting to divorce him. Before she can finish her speech and reveal to Cal that she has feelings for him, he thanks her for babysitting and drives home.
Cal moves into his own small apartment, leaving Robbie and his daughter Molly (Joey King) to live at the family house with Emily while they begin the divorce process. Cal goes to a local bar night after night, talking loudly about his divorce even when no one is listening. His behavior attracts the attention of a young man named Jacob Palmer (Ryan Gosling), a womanizer who beds different women each night. Although the night before Cal showed up a young woman named Hannah (Emma Stone) rejected his advances.
Jacob takes pity on Cal and offers to coach him how to reinvent himself and become a confident man again, which will allow him to pick up women just like Jacob does. While Cal is skeptical of why Jacob wants to help him, he agrees to take his advice. After a makeover and lessons on how to converse with women, Cal seduces a woman named Kate (Marisa Tomei) at the bar with honesty. Kate asks Cal to call her, but having found his confidence for the first time in his life Cal begins to successfully seduce other women at the bar. He sees Emily again at Robbie’s parent-teacher conference. Their interaction goes well until they discover that Robbie’s teacher is Kate, whom Cal never called after their one-night stand. Angered that Cal won’t admit how they know one another, Kate reveals to Emily that she and Cal have had sex. Emily storms out of the parent-teacher conference. Cal catches up to her and confesses to having slept with nine women since their separation. Emily leaves in disgust and begins actively dating David.
Meanwhile, Hannah is expecting her boyfriend Richard (Josh Groban) to propose marriage while they celebrate her passing the bar exam. However, instead of a proposal he offers her a position at his law firm. Offended and hurt, Hannah storms out from the restaurant and returns to the bar where she originally rejected Jacob’s advances. Finding him there she walks right up to Jacob and passionately kisses him, asking if Jacob still finds her attractive and wants to take her home. Hannah takes him by the hand and leads Jacob out of the bar. At his home, Hannah calls Jacob out on his process of seducing women. They playfully banter back and forth, Jacob realizing his standard pick-up lines and techniques don’t fool Hannah. Cal tries to call Jacob but Jacob continually lets the calls go to voicemail. Jacob slowly begins to open up to Hannah as the night goes on; eventually they stay up into the early hours of the morning laughing and talking until Jacob passes out. Hannah kisses him on the cheek before falling asleep herself.
David takes Emily out for a nice dinner together, then walks her to her door to say goodnight. They are interrupted by Jessica, who is babysitting again. Emily tries to introduce David as just a co-worker who took her out for dinner after work but Jessica sees right through it. Emily asks how much she owes Jessica for babysitting and in response Jessica shares with Emily how Robbie and Molly are the only two kids she’s ever babysat that always stay up until their dad gets home. In confusion, Emily asks what she is trying to say; Jessica tells her she does not want her “slutty money” and proceeds to walk home.
Upon arriving home, Jessica decides to take several nude photos of herself to eventually give to Cal on the advice of her classmate Madison (Julianna Guill), who is known to have relationships with older men. Jessica prints and puts the photos into a card and envelope addressed to Cal and hides it in one of her clothing drawers.
Later, Emily calls Cal under the guise of needing help with the house’s pilot light. Cal sees through the ruse because he has secretly been gardening at the family house at night after having a nightmare that David was doing all the yard work himself for Emily. Realizing that she called just because she too was missing him, Cal decides to try and win her back. Jacob finally returns Cal’s calls and asks for advice about being in a real relationship and meeting his girlfriend’s parents, as he is very nervous and never legitimately dated anyone before. Cal tells Jacob to just be himself and everything will be fine.
Jessica’s mother, Claire (Beth Littleford), discovers Jessica’s naked photos addressed to Cal while putting away laundry. She shows them to Jessica’s father, Bernie (John Carroll Lynch). Bernie becomes disgusted and enraged, believing that Cal is preying on his daughter and rushes out of the house to confront Cal. Jessica races after him to try to tell him the truth, that Cal has no idea she is in love with him or anything about the photos.
Cal, with the help of Robbie and Molly, creates a makeshift mini-golf set in their backyard to remind Emily of their first date. The kids lead Emily into the backyard where Cal is waiting. Before Cal can tell Emily how he still feels, Jacob and Hannah show up at the house, and Hannah is revealed to be Cal and Emily’s first daughter born to them right out of high school. Cal is appalled that Jacob is dating his daughter, and immediately forbids her from seeing him. Before Hannah can get an answer on how Cal and Jacob know one another, Bernie shows up and attacks Cal. Jessica arrives as Bernie and Cal wrestle on the ground and tells her father that Cal knew nothing of the pictures or that she was in love with him. Robbie is devastated that Jessica loves his dad, not him. As all this is going on David arrives in the backyard to return Emily’s sweater that she left in his car the previous date night. Jacob asks David if his name is Lindhagen and when David replies “yes,” Jacob punches him in the face for the pain he caused Cal. Cal, Jacob, David, and Bernie then get into a scuffle which is soon broken up by the police. Cal starts spending time at the bar again and receives a visit from Jacob, who confesses that he is in love with Hannah and has begun to re-evaluate his life as a result. Cal replies that he is happy that Jacob is a changed man but does not approve of Jacob and Hannah’s relationship, having seen Jacob’s former lifestyle. Jacob resigns without harboring any ill feelings; rather, he expresses his respect for Cal and praises him for being a great father.
At Robbie’s eighth-grade graduation, Robbie is the salutatorian and begins to give a pessimistic speech about how he no longer believes in true love and soulmates. Cal stops him and instead begins to recount his courtship with Emily to the audience, saying that, while he does not know if things will work out, he will never give up on Emily. With renewed faith, Robbie reaffirms his love for Jessica, to the audience’s applause. After the ceremony, Cal gives Jacob and Hannah his blessing. Jessica gives Robbie an envelope containing the nude photos of herself that were originally intended for Cal to “get him through high school.” Cal and Emily have a laugh talking about the events that have transpired the past year, hinting that they might get back together.