When a nurse downloads an app that claims to predict the moment a person will die, it tells her she only has three days to live. With the clock ticking and a figure haunting her, she must find a way to save her life before time runs out.
At a party, teenager Courtney is convinced by her friends to download Countdown, an app that seemingly predicts how long a user has left to live. Courtney is startled that it says she has only 3 hours to live. After avoiding getting into a car with her drunk boyfriend Evan, Courtney receives a notification stating that she has broken the “user agreement”. Returning home, she is attacked by an unseen entity known as the Angel of Death and killed as her timer reaches zero. At the same time, Evan crashes and a tree branch goes right through where Courtney would have sat.
Quinn Harris, a nurse that works at the hospital where an injured Evan is admitted, suffers frequent sexual harassment by her boss, Dr. Sullivan, but fears speaking out as she has only just passed her exam to be an RA. Quinn stumbles across Evan in a closed-off wing of the hospital where he tells her about Courtney and his suspicions about the app. He also reveals that he downloaded it and it states that he will die at the time he is due to go into surgery. Quinn is dismissive of his claims but eventually downloads the app after her co-workers download it. She is horrified to learn that it says she has only three days left. Evan later skips his surgery and is informed that he has violated the user agreement of the app. He is confronted by a demonic version of Courtney and is killed.
Quinn visits her home to pick up an important document and encounters her younger sister Jordan who has a strained relationship with her following their mother’s death. The next day, Quinn learns of Evan’s death and procures his phone. She cancels a plan to go out with Jordan and their father before being informed that she has broken the user agreement. She is then harassed yet again by Sullivan before fleeing. Quinn researches the app, learning of Courtney’s death and that similar things have happened to other app users although they are widely regarded as fake. She is startled by a vision of a dead Evan and flees her apartment. She is found the next day by Jordan and Jordan learns about the app which states Quinn only has one day left. Increasingly panicked, Quinn buys a new phone but discovers the Countdown app has installed itself on the new phone. After being attacked by a demonic figure, she encounters Matt, whose Countdown app states he will die a few hours before Quinn.
The pair head to the hospital to get help from the hospital’s priest only for Quinn to learn that Sullivan has tricked the staff into thinking that she sexually harassed him; as a result, Quinn is suspended. Matt is attacked by the entity taking the form of his younger brother who died of an illness years ago. The pair leave the hospital and begin to suspect that something in the user agreement may help them. It states the agreement is broken if the user tries to change their fate and they realize that they have canceled plans — Quinn’s trip with her family and Matt taking a train ride — that would result in their deaths. They consult a priest called Father John who states that the app’s code may help them. They hack into the code with the help of a phone salesman and learn that Jordan has downloaded the app and is due to die shortly before Quinn. With the help of Derek, a cellphone shop employee, they hack the app to add more years to all three of their life spans. However Quinn is attacked by the Angel of Death later that night and the countdowns revert back to their original times.
After Jordan is attacked by the demon who takes the form of her mother, the trio consults Father John who identifies the demon and curse via the app code before theorizing that the curse can be broken if someone dies before their countdown ends or lives after. The countdown timer only needs to be beaten by one second, then they’ll win. They prepare a warding circle to protect them from the demon’s attacks but Matt is lured out by the Angel of Death taking the form of his brother. Matt ends up getting hit by a car and killed as his last breath exactly when the app said.
Jordan is also injured in the attack and Quinn takes her to the hospital where she learns that Sullivan also harasses other female staff members. Realizing that she could kill Sullivan and take the 57 years his Countdown app predicted for him, Quinn lures him into the closed-off wing and attacks him but he is saved by the demon who realizes what she is doing. The Angel of Death hunts down Jordan as Quinn searches for Sullivan who escapes after Quinn is injured.
The Angel of Death prepares to kill Jordan as her timer runs out but Quinn overdoses on drugs, sacrificing herself before her time is up and destroying the Angel of Death. Jordan notices that Quinn’s written something on her arm where she drawn herself a circle and the word “Narcan”. Jordan revives her by syringe with Naloxone and their two succeed as the countdown timers for them both stop.
Later, Quinn, Jordan and their father visit their mother’s grave. As they leave, the news about Sullivan’s been arrested after more nurses came forward and told their similar stories of sexual assault. Quinn discovers an update of the app Countdown 2.0 has downloaded itself on the phone.
In a mid-credit scene Derek is on a Tinder date. While his date goes to the bathroom Derek’s phone buzzes, he looks at it and the Countdown app says he has broken the user agreement. The lights in the restaurant go out before he is attacked by the Angel of Death.
The movie opens with a group of friends at a party drinking. They start talking about an app that predicts when you are supposed to die called Countdown. One by one they start sharing the date they were assigned but one of the friends named Courtney (Anne Winters) gets an assigned death time of later that night. After the party, Courtney’s boyfriend Evanis drunk and attempting to drive her home but because of the countdown timer she’s wary to let him drive her home and insists that they walk. Evan gets mad and drives off on Courtney leaving her to walk home alone. She then gets a notification saying that she violated the user agreement of the countdown app. While she is walking we see a cloaked figure following closely behind her but then the figure peels off and gets into a nearby car and drives off. Courtney runs into her house and locks the door and looks outside. She then goes into the bathroom and fills a glass of water, and checks the shower as the countdown app goes off. She drops the glass and then gets dragged into the air vertically and dropped so that her neck breaks across the bathtub. The scene shifts to where an SUV crashed into the woods and we see the driver was Evan, and in the passenger seat where Courtney would have been there is a tree branch that has gone through the truck and into the seat, so Courtney would have died either way. The credits start.
At the hospital, Evan meets Quinn, the main character (Elizabeth Hail) who is a nurse at the hospital. She tries to comfort Evan who is due for surgery and on crutches and in a foot cast. Evan laments the death of Courtney and is conscious of his impending mortality since the countdown app has him dying during surgery.
We meet Quinn’s coworkers who work under head Nurse Amy (Tichina Arnold) and a few of them start downloading the Countdown app and laughing about the time they have. Suddenly a couple come into the hospital room with the girlfriend apparently having overdosed so the staff resuscitates her with a dose of narcan.
We go back to Evan, who is wandering around an under construction area of the hospital to avoid the surgery and we see he gets the user agreement violation. He sees a hooded figure behind him in the hallway mirror and when he looks back it’s gone. The lights start to flicker and he ends up escaping to a stairwell. He sees an apparition of Courtney on the steps and calls her name, but when she turns around her face is decayed and her eyes are yellow. The camera cuts to the bottom of the stairwell and we see Evan fall along with his phone.
Quinn is leaving work for the day and downloads the countdown app and sees she has three days to live but shrugs it off. She stops by her fathers house to get information for her I-9 (work forms) and the tv is on. She hears a noise in the closet and opens it to find her younger sister Jordan (Talitha Bateman). She slides some clothes over to see a bare chested boy and she scolds her sister. We see that the relationship between the sisters is a bit tense, as the younger sister resents that Quinn doesn’t spend a lot of time with her and their father since her mother died. At work the next day, Quinn finds out Evan died and she goes down to where his body is stored to find his phone. She sees the photo of Courtney and him on his home screen and decides to research. Back upstairs, Quinn cancels plans to hang out with her dad and sister and gets the notification that she violated her user agreement. As she walks through the halls a dark figure is in the background of one of the rooms, but when she walks backwards the figure is gone. Then Quinn’s supervisor Dr. Sullivan (Peter Facinelli) lures her to a room under the guise of checking on a patient, but he uses the opportunity to try to pressure her into sex. Quinn turns down his advances but he forces himself onto her before apologizing for his actions. In the hallway Quinn tries to talk to Nurse Amy, but Dr. Sullivan calls her to check on a patient to thwart Quinn.
At her own home Quinn researches the app as well as watches a video about it, and reads comments disputing the video as fake. Then she sees the ghost of Evan which freaks her out and causes her to go sleep in her car. The next day her sister awakens her and they go inside. Their father is out of town and has left Jordan in the care of a family friend, who she has ran away from. Jordan and Quinn get into it after Jordan isn’t allowed to stay over at her sisters and she says she’s going to download the app and invite the boy from earlier in the movie over as she leaves. Quinn goes to buy a new phone from the cell phone store, and freaks out when the app redownloads itself to her new phone, even with a new number, SIM card, and service. In her car, she sees the cloaked figure in the rear view, and ends up backing into somebody’s car when it attacks her. The other driver confronts her and Matt (Jordan Calloway) comes to her defense, as he also was there about the Countdown app. They go to the hospital to talk to the priest and Matt is attacked in the bathroom, while Quinn is confronted by the HR department, as Dr. Sullivan has reversed the story to blame Quinn, and she is subsequently suspended. At a bar they trick another patron into downloading the app so they can review the user agreement, and figure out that changing any plans that were going to result in their death is what violates the user agreement. The two go talk to another priest (P.J. Byrne) who may be able to tell them about the demon stalking them. He tells them that he may be able to help them more if they have the app hacked, so they return to the phone store from earlier and bribe the store manager (Tom Segura) to do it. They add more time to their app, as well as to Jordan’s, since she downloaded the app and is supposed to die three minutes before Quinn. Later that night Matt spends the night with Quinn, and they are both alerted that the countdown clock has reverted back to its original time. Quinn is then attacked by the demon, as well as her sister, who they rush over to save at the babysitters house.
The three return to the priest, who tells them the code of the app is in latin and tells them about a demon from the biblical days who tortured a King for avoiding his death. A Gypsy told the king he was supposed to die in battle and he sent his brother to fight in his place, but the brother did not die. They perform a ritual involving blessing some salt in a ring to keep the demon away. The demon shows up and manages to lure Matt outside of the ring by setting off a deafening alert that everybody can hear except Matt, who is apologizing to the ghost of his dead younger brother, who the demon took the form of during the attack at the hospital earlier. Matt was wracked with guilt for stealing his brothers dinosaur while he was dying at the hospital when they were younger. The brothers eyes turn green and the demon drags him outside with Quinn and Jordan giving chase. Outside they find Matt is ok, but he instantly gets hit by a truck and pinned up against a tree where he dies. Quinn starts crying and begins to accept her fate when she discovers that her sister was impaled in the abdomen during the pursuit of Matt. They rush her to the hospital where Dr. Sullivan tends to Jordan. Quinn is taken aside by another coworker who tells her that she also was sexually assaulted by Dr. Sullivan and that if she wants to step forward legally that she will back her up. Quinn goes into Dr. Sullivan’s office and seduces him to come to the under construction wing of the hospital, where she launches a plan they discussed with the priest, that if somebody dies before they were set to, it will defeat the demon. Quinn tries to inject Sullivan with an overdose of morphine but the demon drags him away as they fight. Jordan shows up and the demon chases her and throws her through a window into another room. Quinn gets the demons attention by beginning to inject herself with the morphine, and the demon changes into the form of her mother and attempts to stall Quinn long enough for the remaining seconds to tick away so it can take Jordan. Quinn resists though and injects herself and causes the demon to turn into ash. Jordan runs over to her collapsed sister and cries over her dead body. Then she notices Quinn had written on her arm a diagram of where to inject narcan, and sees a syringe full of it in her pocket. She injects her and brings Quinn back to life as they hug.
The movie ends with Quinn, Jordan, and her dad at her mother’s grave visiting. As they leave, Quinn gets a new notification…Countdown has finished updating to version 2.0 on her phone.