The figure is at the top end of the scale of losses the company had warned it would bear, after it failed to recruit and train enough of the guards it had promised for the event.
The government was forced to turn to the army for the extra staff needed, for which G4S confirms it will pay.
G4S chief executive Nick Buckles has apologised for debacle.
G4S revealed the cost along with its interim results, where it said half-year pre-tax profits had fallen from £151m to £61m.
The company was contracted to supply 10,400 security guards to the 100 Olympic sites across the country but was unable to find them in time.
G4S said in a statement that it had had 8,000 staff on the ground over the course of the Olympics and that in many cases the military were able to withdraw from specific sites.
A Note to say I'm sorry I'm a perfect world, we would never need to apologize. We would never speak a thoughtless word… or let each other down or break each others heart. Love would conquer all, and happy endings would be time a dozen. But this is not a perfect world , and sometimes people learn things the hard way. we do things we can't take back, no matter how hard we try. I'm sorry for causing you so much pain, for giving you a reason to doubt how much i care, I'm sorry, with all my heart, because I really do care.