Plot

When Lainy's plan to settle down and start a family falls apart, she puts on a fake baby bump, tells a lie and accidentally falls for her dream guy.

As a child, Lainy (Amy Schumer) plays a mom giving birth, with her best friend Kate (Jillian Bell). Lainy believes that being a mother is the greatest thing a human being can do, while Kate doesn't want to be a mother. After they grow up, both are teachers at the same school. Kate is married and becomes pregnant. Kate is married to Mark (Joel David Moore).

When Dave (Damon Wayans Jr.), Lainy's boyfriend of four years, invites her to a fancy dinner, she expects a proposal. However, Dave asks her to participate in a threesome, which leads Lainy to lose her cool. In her class the next day, Lainy again loses her composure as she tells her students that there is no such thing as love, while teaching Romeo and Juliet. She burns her students' books and sets off the fire alarm. Lainy learns about Kate's pregnancy when they meet up for lunch. Lainy reacts very negatively as she thought that she would have the baby first.

Next day at school, Lainy learns that another younger teacher Shirley (Lizze Broadway) is also pregnant. Shriley dresses really inappropriately for school and is almost juvenile in her behavior. Lainy tries to avoid talking to Shirley at a coffee shop by pretending to talk to a stranger. She later finds that his name is Josh and that he has a funny side.

Lainy and Kate go to a maternity clothing store, where she puts on a fake pregnancy belly. She is happy with people in the store wishing her well and treating her with respect. One employee offers to give her a foot massage, while the other brings her a soft beverage. She dons the fake belly and visits a Prenatal Yoga class called "Mamaste", where she befriends Megan (Brianne Howey), a pregnant woman. On the way to the Yoga class, people are really nice to Lainy, give her fruit, make way for her, give her seats on the subway and so on.

Kate and Shirley throw a joint gender reveal party, which really irritates Lainy. Shirley selects Lainy to whack a stuffed toy baby to do the big gender reveal. Lainy hits the toy really hard which strikes her co-worker Fallon and throws her into the pool.

Megan invites Lainy to her home for dinner, where she again meets her brother Josh (Will Forte) (who she first met at a coffee shop) and husband Steve (Chris Geere). Josh is surprised to see that Lainy is pregnant as she did not seem that way just a few weeks ago. Lainy tells Josh that she is single, and the baby was a result of a one-night stand. Josh operates the Zamboni at a local ice-skating rink.

Her belly accidentally catches fire. While patching it up, she talks to Megan for a while, who thanks Lainy for giving her strength, so Lainy continues faking her pregnancy. Megan says that after her first kid was delivered, she started bleeding a lot and there was a moment when she thought that she could die. Megan says that seeing Lainy go through her pregnancy gives her the strength to face her 2nd delivery.

Lainy's co-worker, Fallon (Urzila Carlson), is aware of her faking her pregnancy and tells her to stop, but Lainy does not listen. At a children's store, Megan's son sees Lainy and Kate and observes the lack of baby belly. Steve and Megan are also there, but Lainy hides so they cannot see her.

Kate tells Lainy that she does not want Lainy in the delivery room with her. Kate says that Lainy is livid because Kate got pregnant first.

Josh calls Lainy for a date on an ice-skating rink and then on a City Cruises Yacht dinner and dance. They bump into Dave, her ex-boyfriend, who believes her when she says she got pregnant during a Thanksgiving Black Friday sale.

Megan visits Lainy at her school, inviting her to join her at a therapeutic class for pregnant women. Lainy grabs a helium balloon and puts it beneath her dress to make it appear as if she is pregnant. Fallon also shows up at the class, pretending to be pregnant.

When visiting Megan to babysit her son, Lainy is attracted to Josh when she sees him reading a book to Megan's son Connor. Lainy kisses Josh and goes to the garage which is where Josh stays. Before they have sex, she covers Josh with an eye mask and keeps her shirt on to keep her fake pregnancy from being discovered. They have sex in the cowgirl position (as Lainy simply cannot get into any other position due to her huge belly), during which the garage door opens by mistake when Lainy presses the remote and are seen by the neighbors walking by the house. After Josh admits he feels he can really trust her and believes they could make it together with the baby, she then abruptly leaves, saying she cannot continue with him.

Lainy confides to Fallon about getting rid of her (non-existent) baby and is overheard by Shirley who tells Kate about it. Kate invites Lainy to her baby shower, where Megan, her husband and Josh arrive upon Shirley's invitation. Shirley announces on mike that Lainy is thinking of getting rid of her baby and asks everyone to convince Lainy not to do that.

Lainy places a roast chicken up her dress to keep up the fake pregnancy, but when confronted about it, drops the chicken and tells everyone she is not really pregnant, whereupon the upset Megan and Josh leave.

Kate and Megan both reconcile with Lainy. She finally tells Josh she loves him and her real name. Dave visits Lainy, who first lies to him saying he is going to be the father of triplets and then watches his relief when she removes her fake pregnant cushion.

Kate delivers her baby with Lainy in the delivery room. Lainy goes back to teaching when one of her students tells her there is a Zamboni outside. They all go out to meet Josh, who confesses his love for her. They ride the Zamboni, accidentally causing extensive property damage on the way out of the school.