Cameron sees the Games in London as a once in a generation opportunity to showcase Britain as a place to do business. The government is running a series of industry summits during the Games to back its sales drive.
"I am confident that we can derive over 13 billion pounds benefit to the UK economy over the next four years as a result of hosting the Games," Cameron said.
"I am certain that when you add in the benefits from construction the total gain will be even greater," he added in a speech at the British team's pre-Games camp in Loughborough, central England.
Britain's economy is back in recession and badly in need of a boost.
Britain has ploughed around 9 billion pounds ($14 billion) of public money into building venues for the July 27-Aug. 12 London Games and providing security. Organisers are also raising a further 2 billion pounds to stage the Games through sponsorship, ticket sales and other activities.
A study by Lloyds Bank published this week found the Games would contribute 16.5 billion pounds to the economy by 2017.
Construction and tourism would be the two sectors to gain most, the study said. However, it noted that most of the economic benefit stemmed from building projects ahead of the Games which are now largely complete.
Most economists say the Games will provide a short-term fillip to the economy but that the impact will be relatively small and swiftly drowned out by broader economic developments.
Marketing restrictions should be lifted as soon as possible after the Games to allow British companies to trumpet work they have done on the project, a report by the head of Britain's Olympic Delivery Authority, the body in charge of developing and building venues for the Games, said on Thursday.
The suppliers have been affected by International Olympic Committee rules designed to grant sponsors exclusive rights to market themselves as backers of the Games. ($1 = 0.6419 British pounds)