The film opens with Matthew Logelin (Kevin Hart) speaking at a funeral for his wife Liz (Deborah Ayorinde). His best friends Jordan (Lil Rel Howery) and Oscar (Anthony Carrigan) try to help, as does Matt’s mother Anna (Thedra Porter), but he is inconsolable. On top of all this, Matt is now a single father to his and Liz’s infant daughter Maddy, and almost nobody – including Matt himself – believes he is ready to take on those responsibilities all alone.
A flashback shows Matt and Liz being told by the doctor that they are going to get their baby out sooner than expected via C-section. The procedure is a success, and Maddy is born a healthy baby girl. Liz’s parents Marion (Alfre Woodard) and Mike (Frankie Faison) come to visit to see their granddaughter. Later on, when Matt tries to help a nurse take Liz to another room, Liz begins to have trouble breathing and starts to lose consciousness. Doctors rush in and send Matt out, but when he sees them again, the doctors say that Liz suffered a pulmonary embolism and has passed away.
Anna and Marion stay with Matt to help take care of Maddy for the time being. Both of them think that Matt should move back to Minnesota to be closer to Marion and Mike, and so he can get a job and raise Maddy there, but Matt doesn’t feel that he can uproot his life so easily. He works with Oscar at an ad agency, and their boss Howard (Paul Reiser) encourages Matt to take time off, even though Matt opts to try working from home.
The first few months caring for Maddy are rough on Matt, with her excessive crying, constant pooping/puking, and uncertainty with how to work strollers and build cribs. He resorts to bringing Maddy to work since he can’t find a babysitter, and both Anna and Liz’s parents have gone back home.
When Maddy won’t stop crying, Matt tries a number of remedies, like rocking her to sleep, singing a lullaby, or feeding her, but none of them work. After attending a support group for new parents, he finds that playing white noise helps her stop and go to sleep. Later, Matt brings Maddy to work during a meeting with important clients. When he hears Maddy crying, Matt rushes out of the meeting to try and stop her. However, the clients are more than understanding and offer Matt tips like downloading a white noise app and utilizing skin-to-skin contact to keep Maddy soothed.
Matt hires a babysitter for the night while he and Jordan go out to the club. When Jordan tries to bring Matt’s attention to some women there, Matt gets upset since he is still not over Liz.
Matt takes Maddy to Minnesota to spend time with her grandparents. They go to Liz’s parents’ home, where they have set Liz’s old room up for Maddy in case she comes over. Matt later visits Anna and expresses his desire to be as great a parent as she was, and she assures him that he is.
Years pass, and Maddy (now played by Melody Hurd) is about 4 or 5 years old. Matt has enrolled her at a private school, but they go against the dress code and have her wear pants instead of skirts like the other girls. She also frequently joins her dad when Jordan and Oscar come over to play poker.
Matt takes Maddy to the park for a birthday party. There, he meets a woman named Lizzie (DeWanda Wise), who is there because Oscar and his wife Rose (Holly Gauthier-Frankel) want to set Matt up with her. When they realize what is going on, they just play along with it and engage in natural conversation. She tells him that she is an animator for a show called “Lucky Jim”, which Matt says Maddy is a fan of. Turns out he was unaware that “Lucky Jim” is NOT a kids program, as it is about a perverted leprechaun named Jim who always gets “lucky”. When Matt sees an episode, he declares Maddy can’t watch it anymore.
Maddy is teased at school by the boys for wearing pants, which gets to the point where the school’s head nun has to tell Matt about the dress code. When going to buy new clothes for Maddy, she tells him she wants Batman boys underwear instead of ones for girls.
Matt later agrees to go out with Lizzie. They have a good time together, and end up sharing a kiss. They eventually start dating consistently, until Matt decides it might be time for Maddy to meet Lizzie, especially since Maddy has felt a bit upset over not having a female figure in her life. After a day at the carnival, Matt introduces Maddy to Lizzie, who tells the girl that she can call her “Swan” instead. Soon, Maddy takes a liking to Lizzie.
The next day, Matt drops Maddy off at school and rushes off to have sex with Lizzie. At school, the boys tease Maddy again when she starts to wear a skirt and they see her wearing boys underwear. When she tries to jump off and tackle one of the boys, she hits her head and gets a nasty gash on her forehead. The school tries to reach Matt, but he eventually checks his phone and rushes to the hospital. He tries to take Maddy away, but the doctors say that she needs stitches. Matt tries to decline since it’s the same hospital where Liz died in and he doesn’t trust the doctors there, but he relents and lets them work. Feeling bad over neglecting Maddy, Matt breaks things off with Lizzie.
At work, Howard tells Matt that he wants to send him to Croatia for a job. He prepares to take Maddy to Minnesota to spend time with her grandparents, but she starts to get mad at him for breaking up with Lizzie and for not letting her see other family. When Maddy gets to Marion and Mike’s home, she asks Marion what her mom was like. Marion says that she was strong and smart, just like Maddy. Matt later sees that Marion wants Maddy to stay with them more long-term, which Maddy seems more open to, but Matt thinks that Marion is just reminding him that he’s making too many mistakes on his own with her, and he tries to take Maddy to go, even though she wants to stay with Liz’s parents. Matt then realizes he isn’t keeping Maddy happy, so he agrees to let her stay there for now. While Maddy sleeps, he expresses to her his fears about raising her on his own.
Matt returns home alone and is later told at work by Howard that he is retiring and recommended Matt for his old job. Matt is thankful, even though this means he might be seeing Maddy even less. Even Jordan and Oscar can see that her absence is making Matt feel worse. While going through her room, he finds a necklace from Liz that Maddy had been desperately searching for earlier. When Matt and Oscar head to Croatia for the job, Matt thinks about Maddy too much and decides to bail on the trip to return to her. She hugs her dad and he gives her the necklace. When it is time to go, he bids farewell to Marion and Mike, the former tearing up as she mentions how happy Matt made Liz.
Matt and Maddy then to go Lizzie’s house where he apologizes to her for how things turned out. She forgives him and agrees to join him and Maddy for ice cream.
During the credits, Matt brings Maddy back to school (just for the rest of the year), where they are allowing her to wear jeans, and he shows up in a skirt to make her feel better.