As a child, Lainy (Amy Schumer) and her best friend Kate (Jillian Bell) often playfully acted out the role of mothers giving birth. Fast forward to adulthood, both have become teachers at the same school, but their lives are taking very different paths. Kate is married and has just announced her pregnancy, while Lainy finds herself facing a relationship crisis. When her boyfriend Dave (Damon Wayans Jr.) of four years unexpectedly invites her to a dinner where he suggests a threesome, Lainy reacts with frustration, anticipating a marriage proposal instead.
The situation escalates the following day in her classroom when Lainy loses her composure and burns her students' textbooks, triggering the fire alarm. Later, during a lunch meet, she discovers more shocking news: another teacher, Shirley (Lizze Broadway), is also pregnant. This prompts Lainy to explore her own feelings about pregnancy. The next day, she and Kate venture into a maternity clothing store. Here, Lainy playfully dons a fake pregnancy belly and enjoys the newfound respect she receives from strangers on the street. Her antics lead her to a Prenatal Yoga class called "Mamaste," where she befriends Megan (Brianne Howey), a pregnant woman who later invites her over for dinner.
At Megan's home, Lainy's fake belly hilariously catches fire, leading to a moment of bonding as she shares uplifting sentiments with Megan who appreciates Lainy for her support. However, as her fake pregnancy story starts to spiral out of control, Lainy's coworker Fallon (Jackie Sandler) warns her to come clean about her ruse, but she dismisses the advice.
The situation grows even more complicated when Josh (Will Forte), Megan's brother, asks Lainy out on a date for ice skating followed by a romantic dinner on a City Cruises Yacht. They unexpectedly encounter Dave, her ex-boyfriend, who buys Lainy's lie about being pregnant.
The tension escalates when Megan invites Lainy to join her therapeutic class for expecting women, and she starts using creative props—like a helium balloon shoved beneath her dress—to maintain the facade. Eventually, during a visit to babysit Megan's son, a romantic moment ensues between Lainy and Josh. However, she goes to great lengths to hide her deception, leading to an awkward encounter where her fake pregnancy is nearly exposed.
When Lainy confesses her supposed plans for abortion to Fallon, her words reach Shirley, who shares the gossip with Kate. Prompted by this, Kate invites Lainy to her baby shower, which Megan and Josh also attend, creating an even more tangled web of lies. As the truth starts to unravel, Lainy finds herself in a comical predicament with a roast chicken in her dress intended to support her act of being pregnant.
Ultimately, the truth comes out in a dramatic scene, leading to tension with Megan and Josh. Fortunately, both Kate and Megan eventually reconcile with Lainy, allowing her to become more honest about her feelings. After a series of misunderstandings and comical situations, Lainy professes her love for Josh and reveals her real identity to him, leaving behind the charade of her fictitious pregnancy.
The film concludes with Lainy returning to her teaching job, where a student alerts her to a Zamboni outside, where the film's romantic climax occurs. Josh professes his love again, leading to a fun-filled adventure as they ride the Zamboni together, causing some unintended chaos that encapsulates the unpredictable and humorous tone of their burgeoning relationship.
