The singer's dad Jamie, who is co-conservator of her estate, allegedly calculated the sum after examining his daughter's bank statements.
A source told In Touch: “It’s staggering how much money has been used up since February 2007.”
Spears is believed to have spent a fortune on legal bills and psychiatric care since her well-documented problems began when she shaved her head last year.
LA-based accountant Robert Bianchi estimated that she may also have missed out on around $50 million by failing to tour with her latest album Blackout.
However, another insider claimed that Spears's financial situation is beginning to improve, saying: “It’s been quite a challenge getting things under control. But now she’s spending about a fifth of what she used to.”