Kutcher was born February 7, 1978 in Cedar Rapids, Iowa, the son of Diane Kutcher (née Finnegan), an employee of Procter & Gamble, and Larry Kutcher, who worked at a General Mills factory. He is of part Irish ancestry on his mother's side. Kutcher has an older sister, Tausha, and a fraternal twin, Michael, who had a heart transplant when the brothers were young. Kutcher's childhood was that of a rugged, outdoorsy Midwesterner, and he had various odd jobs, including carpentry, and other jobs relating to farm life.
Kutcher attended Washington High School in Cedar Rapids, Iowa for about a year when his family moved to Tiffin, Iowa, where he attended the Clear Creek-Amana High School. In addition to being a student, he played on the football team as a wide receiver and appeared in school plays. Meanwhile, his home life was stressful. He has stated that "I didn't want to come home and find more bad news about my brother" and "kept myself so busy that I didn't allow myself to feel." Kutcher admitted that as a teen, he contemplated committing suicide. At thirteen, he attempted to jump from a hospital balcony, but his father intervened at the last minute. At around this time, his parents divorced. During his senior year, he broke into the high school at night with his cousin in an attempt to steal money; he was caught leaving the scene. Kutcher was convicted of third-degree burglary and sentenced to three years' probation and 180 hours of community service. Kutcher stated that though the experience "straightened him out", he lost his girlfriend and anticipated college scholarships, and he was ostracized at school and in his community.
Kutcher attended the University of Iowa, where he majored in biochemical engineering (but did not receive a degree), motivated by the desire to find a cure for his brother's heart ailment. At the University of Iowa, Kutcher was kicked out of his apartment for being too "noisy" and "wild". Kutcher stated, "I thought I knew everything but I didn't have a clue. I was partying, and I woke up many mornings not knowing what I had done the night before. I played way too hard. I am amazed I am not dead." He was a member of the Delta Chi fraternity. To make ends meet, Kutcher worked as a college summer hire in the cereal department for the General Mills plant in Cedar Rapids, and sometimes donated blood for money. During his time at the University he was approached by a scout at a bar called The Airliner in Iowa City, Iowa, and was recruited to enter the "Fresh Faces of Iowa" modeling competition. After placing first, he won a trip to New York City to the International Modeling and Talent Association (IMTA) Convention. Following his stay in New York City Ashton returned home to Cedar Rapids, Iowa before relocating to Los Angeles to pursue his acting career.
After participating as a modeling contestant in an IMTA competition (losing to Josh Duhamel) in 1998, Kutcher signed with the Next modeling agency in New York, appeared in ads for Calvin Klein, modeled in Paris and Milan, and appeared in a Pizza Hut commercial.
After some success in modeling, Kutcher moved to Los Angeles and, after his first audition, was cast as Michael Kelso in the television series That '70s Show, which debuted in 1998 and ended in 2006. Kutcher was cast in a series of film roles; although he auditioned but was not cast for the role of Danny Walker in Pearl Harbor (2001), he starred in several comedy films that performed well at the box office, including Dude, Where's My Car? (2000), Just Married (2003), and Guess Who (2005). In addition, he appeared in the family film Cheaper By The Dozen, playing a self-obsessed actor. His 2004 film The Butterfly Effect was an unusually dramatic role for Kutcher, playing a conflicted young man who fell in love with a girl called Kayleigh; the film received very mixed reviews, but was a box-office success.
In 2003, Kutcher produced and starred in his own series on MTV's Punk'd as the host. The series involved various hidden camera tricks performed on celebrities. Kutcher is also an executive producer of the reality television shows Beauty and the Geek, Adventures in Hollyhood (based around the rap group Three 6 Mafia), and The Real Wedding Crashers and the game show Opportunity Knocks. Many of his production credits, including Punk'd, come through Katalyst Films, a production company he runs with partner Jason Goldberg.
Because of scheduling conflicts with the filming of The Guardian, Ashton was forced not to renew his contract for the eighth and final season of That 70s Show, though he did appear in the first four episodes of it (credited as a special guest star) and returned for the show's series finale.
Kutcher is part of the management team for Ooma, a tech start-up launched in September 2007. Ooma is in the Voice over Internet Protocol business and Ashton's role is as Creative Director. He's spearheading a marketing campaign and producing viral videos to promote this service. Kutcher has also created an interactive arm of Katalyst called Katalyst Media with his partner from Katalyst Films, Jason Goldberg. Their first site is the animated cartoon, Blah Girls.
Kutcher is due to produce and star in the action comedy Five Killers, in which he will play a hitman.
Kutcher dated actresses January Jones (from 1998 to 2001), Ashley Scott (from 2001 to 2002), Monet Mazur (2002), and Brittany Murphy (from 2002 to 2003). Following his break-up with Murphy in early 2003, Kutcher began dating Demi Moore; reports in the media frequently commented on the sixteen-year age difference between the two. Moore and Kutcher married on September 24, 2005 in a private ceremony conducted by a rabbi of the Kabbalah Centre; the wedding was attended by about 100 close friends and family of the couple, including Bruce Willis, Moore's ex-husband.
Both Kutcher and Moore are followers of the Kabbalah Centre,
a controversial California-based organization which alleges that it teaches Kabbalah, a form of Judaism. As part of his involvement in Kabbalah, Kutcher has toured Israel with Demi Moore, as well as taken time off to observe traditional Jewish High Holy Days, and celebrated the Jewish holiday Purim. Kutcher also usually wears the traditional Kabbalah Red string.
Kutcher remains friends with his former That '70s Showco-stars Danny Masterson
and Wilmer Valderrama, and actor Seann William Scott, his costar in Dude, Where's My Car?. Kutcher has invested in an Italian restaurant named Dolce (other owners include Masterson and Valderrama) and a Japanese-themed restaurant named Geisha House located in Atlanta and Los Angeles. Kutcher is a Chicago Bears fan.
Kutcher's former girlfriend, Ashley Ellerin, a 22-year-old fashion model, was found stabbed to death in her Hollywood Hills apartment in February 2001. Hours before she was found dead, Kutcher visited her home to pick her up for the 43rd Grammy Awards, but no one answered the door. Kutcher looked inside her apartment through a back window and saw what he thought were red wine stains on the carpet, then left. Ellerin's body was found later in the day by her roommate, and after hearing of the news, Kutcher went to the police to offer any help in the investigation. In August 2008, police announced that they had traced Ellerin's murder to suspected serial killer Michael Gargiulo, a Santa Monica resident who is charged in the stabbing deaths of at least three women.
On April 16th, 2009, Kutcher became the first user of social networking site Twitter to have more than 1,000,000 followers , beating out CNN in the "Million followers contest".  He previously announced that he would be donating $100,000 to a charity to fight malaria, and displayed the check on Ustream.tv. He has also announced his plans to ding-dong ditch media mogul Ted Turner.