The Big Bang Theory has been highly rated since its premiere. When the third season premiered on September 21, 2009, The Big Bang Theory ranked as CBS's highest-rated show of that evening in the adults 1849 demographic (4.6/10) along with a then-series-high 12.83 million viewers.[97] After the first three seasons aired at different times on Monday nights, CBS moved the show to Thursdays at 8:00 ET for the 20102011 schedule, to be in direct competition with NBC's Comedy Block.[98] During its fourth season, it became television's highest rated comedy, just barely beating out eight-year champ Two and a Half Men. However, in the age 1849 demographic (the show's target age range), it was the second highest rated comedy, behind ABC's Modern Family. The fifth season opened with viewing figures of over 14 million.[99]
The sixth season boasts some of the highest-rated episodes for the show so far, with a then-new series high set with "The Bakersfield Expedition" (Season 6, Episode 13), with 20 million viewers,[100] a first for the series, which along with NCIS, made CBS the first network to have two scripted series reach that large an audience in the same week since 2007. In the sixth season, the show became the highest rated and viewed scripted show in the 1849 demographic, trailing only NBC's Sunday Night Football coverage,[101][102] and was third in total viewers, trailing NCIS and Sunday Night Football.[103] Season seven of the show opened strong, continuing the success gained in season six, with the second episode of the premiere, "The Deception Verification", setting the new series high in viewers with 20.44 million.[104][105]
Showrunner Steve Molaro, who took over from Bill Prady with the sixth season, credits some of the show's success to the sitcom's exposure in off-network syndication, particularly on TBS, while Michael Schneider of TV Guide attributes it to the timeslot move two seasons earlier. Chuck Lorre and CBS Entertainment president Nina Tassler also credit the success to the influence of Molaro, in particular the deepening exploration of the firmly established regular characters and their interpersonal relationships, such as the on-again, off-again relationship between Leonard and Penny.[106] Throughout much of the 201213 season, The Big Bang Theory placed first in all of syndication ratings, receiving formidable competition from only Judge Judy and Wheel of Fortune (first-run syndication programs). By the end of the 201213 television season, The Big Bang Theory had dethroned Judge Judy as the ratings leader in all of syndicated programming with 7.1, Judy descending to second place for that season with a 7.0.[107]