The G4S Olympic contract amounted to £284 million, in return for which G4S would provide 10,400 security personnel. Of this amount, £57 million was in the form of a "management fee".
Presumably therefore £227 million was earmarked for the supply of personnel (incidentally amounting to about £22,000 per employee).
G4S is now aiming at the provision of only 7,000 personnel, a 33% shortfall (although it cannot guarantee even this reduced provision).
Accordingly, and assuming that the contract is on a broadly pro rata basis, G4S remuneration faces a reduction of £75 million (33% of £227 million). Its management fee of £57 million must also be in doubt, and then it also has to pay for the extra soldiers and police now to be committed to the Games.
It is therefore facing a loss on the contract of well over £100 million. So why is the company talking of a loss of only £30 million to 50 million?
(Basic figures taken from this article.)