Produced on an estimated budget of ₹200 crore (US$28 million), Zero is Khan's most expensive film. The film was conceived by Rai in 2012, after he was inspired by the superhero genre. Pre-production began in 2016. Initially titled Katrina Meri Jaan, Zero went through numerous title changes before arriving at the final title in early 2018. Principal photography of the film began in Mumbai on May 2017. It marked the last film appearance of Sridevi, who died shortly after completing the film. Filming commenced in 2018 at Orlando. The film's soundtrack is composed by Ajay-Atul with lyrics written by Irshad Kamil. Zero is set to be released on 21 December 2018.
Bauua Singh is a vertically challenged man from Meerut who faces difficulty falling in love. He finds his companion in Aafia Bhinder, a NASA scientist with cerebral palsy; however, leading female superstar Babita also gets close with him, testing his first relationship. A love triangle forms between the three, taking them to far-off cities, and thrusting Bauua on an adventure to discover both his true love and the measure of a man's true worth.
"Like the way we say that perfect is boring, imperfection is much interesting... Our film is also celebrating the same. The story of the film is celebrating a perfect love story of two imperfect people. Though the protagonist of the film is a dwarf but more than the physical disability of an individual, the story talks about the space of emotional incompleteness of our life."
Aanand L. Rai on the decision to name the film Zero and its implications
Director Aanand L. Rai conceived the film in 2012 after watching Krrish and drawing parallels of the titular character with that of American superheroes such as Spider-Man, Batman and Superman. He appreciated the achievements of Indians having their own superhero film but felt wary of the outreach, saying, "I loved seeing Hrithik Roshan fly off a 250-feet building, it was brilliantly done, but deep down I felt this wasn’t us. Apart from our mythological demigods, Indians aren’t ready for superheroes, we are still short in height. That’s what made me want to live life from the perspective of a dwarf [[sic]]."
The film was initially titled Katrina Meri Jaan. However, this was later scrapped because the producers thought the title would be too misleading to people and make them presume the film is about Kaif. In between productions, the film underwent through numerous working titles such as Bauaa, Bauna, Butka, Bandhua and Batla. Red Chillies Entertainment registered three names for use as the film's title. In the end, a unanimous decision was made to call the film Zero, revealed in January 2018.
Bollywood Hungama reported the budget of the film to be around ₹150 crore. Rai refuted these reports and stated that the film did have a big budget at that time, but less than the reported amount, and that the amount might change. In October 2018, after post-production work was completed, the film's budget was revealed to be ₹200 crore, making it the most expensive film starring Khan.Himanshu Sharma, who wrote the script, confirmed the story to be a romantic drama. He stated that while the story does feature a little person as a character, the plot does not revolve only around that character.
Initially, Salman Khan was approached for the role in 2012. The role then went to Shah Rukh Khan. His casting was confirmed in March 2016. He plays a three-four foot physically challenged man. Rai cast Khan to play the lead role because he needed a big star for the story to penetrate globally. He needed "an intelligent actor, who also can carry that happy-go-lucky attitude," and he felt Khan possessed those qualities. Rai realised the difference between a six-foot tall person saying "I love you" and a four foot tall person; hence he hired Khan. Khan is the fifth actor of normal stature in Indian cinema to play a little person after Kamal Haasan in Apoorva Sagodharargal (1989),Johnny Lever in Aashiq (2001), Jagathy Sreekumar in Athbhutha Dweepu (2005) and Anupam Kher in Jaan-E-Mann (2006).
After much speculation, Rai confirmed Anushka Sharma and Katrina Kaif as the female lead actors in the film in June 2017; this would be the second collaboration between the two actresses and Khan after their 2012 film Jab Tak Hai Jaan. Kaif was cast after Salman Khan suggested her. Sharma was reported to play a differently-abled person, whereas Kaif confirmed that she will portray the role of an actress. Both Sharma and Kaif were offered the role not because of their stardom but because they fit the role according to Rai. According to Kaif, she was offered the film before Khan was cast. She was initially supposed to play herself in the film, but the character was later revised to be a satirical take on herself. She later confirmed that the script and story of Zero had changed over two years, hinting that Khan recommended this.Tigmanshu Dhulia will portray Khan's father. He showed interest in the project after hearing about its heavy technical involvements. Khan refrained from signing any other film during Zero's production. The film features guest appearances by Salman Khan, Rani Mukerji, Deepika Padukone, Kajol, Alia Bhatt, Sridevi, Karisma Kapoor and Juhi Chawla who will portray themselves. This will mark Sridevi’s last appearance in a film, as she died before the film's release shortly after filming.
In August 2016, it was said that filming would begin in December 2016. This was later postponed to 2017.Principal photography of the film eventually began in May 2017 in Mumbai. In May, an accident occurred on the set, in which crew members were injured. In June 2017, Khan revealed that only 10 minutes of footage had been completed. Kaif joined the team on 22 September 2017. Sharma started shooting in September. On 8 January, she resumed her shooting after taking a break for a couple of weeks for her wedding. Two days later, Khan was photographed on the sets of the film in suburban Mumbai. The crew took a break during the Makara Sankranti festival. The shoot was also extended to Bandra, Mumbai. Around January 2018, Kajol completed filming for her cameo. Parts of the film were also shot in Dubai.
Visual effects were heavily used to make Khan's character three feet tall. According to Khan, this was done as "I would have a problem if I have to do it on my knees. I am trying to avoid that part because that looks unreal also, and in today’s time and age, you don’t want to do that." The makers took inspiration from the technology used in The Lord of the Rings. The character was shot using Forced Perspective, which according to NDTV, is "a technique that employs optical illusion to make an object appear farther away, closer, larger or smaller than it actually is. It will make SRK look shorter." According to Rai, the film will use the most visual effects for an Indian film. Most of the film was filmed entirely in Film City. In February 2018, it was reported that the post-production work of a second teaser was being carried out. From 4–8 April 2018, Khan shot the film's schedule in Vasai, Mumbai, flying in a helicopter to avoid the traffic. In middle April, the film's shooting was reported to shift to the United States for a sequence. Some sequences were also filmed in Alabama. Khan finished filming for Zero, and wrapped the film's principal photography in Orlando, during the month of June 2018.
The title of the film was announced by Khan and Rai on 1 January 2018 in a minute long teaser posted on Twitter due to robust demand from fans. The video showed Khan in his dwarf avatar singing and dancing to Mohammed Rafi's "Hum Ko Tum Pe Pyar Aaya". Although neither Kaif nor Sharma appeared in the teaser video, in one of the scenes, Khan wore a jacket with a collage of Kaif's pictures imprinted on it. In less than 24 hours, the video garnered over 3 million views on YouTube alone, and Khan's announcement tweet had over 30,000 likes. Red Chillies Entertainment later announced that Zero-related posts had reached over 10 million views, likes and mentions across various social media platforms like Facebook, YouTube, Twitter and Instagram. The following day, the first teaser poster with the tagline "21st December 2018 se aapke piche" was unveiled by Red Chillies Entertainment, revealing that the film would release on 21 December 2018.
According to Rai, Zero was chosen to be released in December since it is "a month when we celebrate life and what better time for a boy who celebrates that he is physically incomplete and in his incompleteness completes others as he travels from Meerut to New York. There is a beauty in incompleteness we are celebrating." During the Islamic festival of Eid, a promotional teaser was released on 13 June 2018, featuring Shah Rukh and Salman, the latter in the attire sported by him in the film Tiger Zinda Hai (2017). In late August 2018, Rai confirmed to news agency Bollywood Hungama that the trailer for Zero would release on 2 November, Khan's birthday. In late October 2018, as part of the promotional campaign, a verified Twitter account emerged in the name of Bauua, Khan's character from the film, featuring the cartoon version of Bauua Singh's first look and posting humorous tweets.
On 1 November, the day before the release of the trailer, two official posters were revealed by Khan on his social media pages: one featuring Khan's character Bauua Singh and Anushka Sharma's character in Connaught Place in New Delhi, and another with Singh and Katrina Kaif's character in front of Meerut's clock tower.
On the morning of 2 November, Director Aanand L. Rai released a third poster on his Twitter page, depicting Khan's Bauua Singh standing on a street near Broadway in New York City. The same day, Red Chillies Entertainment released the official trailer on YouTube. The trailer recorded more than 54 million views within 24 hours. On 10 November, Zero's trailer was screened at the 24th Kolkata International Film Festival in the presence of Khan and West Bengal Chief Minister Mamta Banerjee.