Jai Verma (Sidharth Malhotra) and Diya Kapoor (Katrina Kaif) are childhood sweethearts. Jai is a maths professor and Diya, an artist. While Jai hopes to get a fellowship at Cambridge University, Diya wishes to get married to her long-term boyfriend. Jai agrees to get married reluctantly but the thought of saat pheras and the billion rituals, as well as the fear of weddings ending in divorces, make him change his mind. Jai criticizes these meaningless rituals and talks negatively of his marriage. He tells Diya that he has other plans for his bright future and she may not be a part of it. She walks away heartbroken. Jai gets drunk and passes out only to wake up in Thailand on his honeymoon. He discovers that it's been ten days since he got married to Diya. He has no memory of it at all. Next up, he wakes up in Cambridge, only to find his wife about to deliver their child. He discovers that it has been two years since his marriage. He realises he has been time travelling and has no control over it.

Next time he wakes up, he is a professor at Cambridge University, his dream job. It has been eighteen years since his marriage. To his horror, Jai realises that it is the day when he and Diya are divorced. Heartbroken, he returns home and pleads to return to the past to set things right. Jai wakes up the next day, realizing he is in the past, seven years after his marriage. He juggles many priorities of his family and career. However Jai gives more priority to work and instead of going for Diya's first art exhibition, he goes to his friend Chitra's (Sayani Gupta) place to help her with her breakup. Chitra tries to have an affair with Jai. Believing it to be the cause of his divorce, Jai hastily returns home, but his family is unhappy with him.

Jai is however convinced that he has set things right. The next day, he wakes up to find himself in his 60-year-old self. He finds out that his mother had died and everyone gathered for her funeral. After the funeral, Jai is shocked that he and Diya are still divorced and that Diya had married another man who enjoyed the love of Jai's mother (Sarika) and children.

Reeling from this blow, Jai comes across the priest (Rajit Kapoor) who had conducted his marriage, who warns him of the importance of time. Jai is given another opportunity to set things right as he goes back in time to the same day, seven years after his marriage. This time, he sets things right. He spends time with his children, does his work well and makes Diya feel special and attends her art exhibition. At the end of the day, Jai is a happy man.

Jai wakes up back into the present, the day after he argued with Diya about his life and his career. Jai rushes back to her, cherishing every moment along the way, also glad to see his mother again, seemingly back from the dead. Jai reconciles with Diya and promises to be true to her. The film ends with both getting married and everyone dancing.