IT beats The Exorcist (and will The Sixth Sense) in terms of unadjusted gross, but taking into account inflation it doesn’t come close; in 2017 dollars, The Exorcist made $1.3 billion domestically and $2.4 billion worldwide – numbers IT can’t even come close to a fraction of.
IT still falls short of M. Night Shyamalan’s The Sixth Sense, which netted $293M domestically and $672M worldwide (per Box Office Mojo) upon its initial release in 1999; Pennywise has obviously not matched either of those amounts.
IT passing The Exorcist was announced by Warner Bros. themselves, who not only has an investment in the new film’s success, but also the classic one’s legacy; they distributed The Exorcist, whereas The Sixth Sense came from Buena Vista (a subsidiary of Disney).
Reports have been suggesting that IT is now the highest-grossing horror film of all time – both domestically and worldwide – but that isn’t actually the case.