The Dreamliner project has been hit by a number of delays
The first flight of the Boeing 787 Dreamliner will take place by the end of 2009, the company has announced.
Boeing also said it hoped to deliver the first plane for service in the last quarter of 2010.
There has been a series of delays in the development of the aircraft, and it is now running almost two years behind its original schedule.
Boeing chairman Jim McNerney said the extra time would enable the remaining work to be completed.
"The design details and implementation plan are nearly complete, and the team is preparing airplanes for modification and testing," he said.
The delay was partly caused by an area within the side-of-body section of the aircraft which needed to be reinforced, Boeing added.
The latest delay in the project, announced in June this year, was the fifth time the launch had been put back.
The company estimated that the cost of the first three test planes, which have no commercial value, would be $2.5bn. This, it said, would be included as a one-off charge in its July to September results.
"This charge will have no impact on the company's cash outlook going forward," Boeing said.
While analysts generally welcomed Boeing's announcement, some cautioned that future delays may still have to be announced.
"Risk remains the new schedule could slip given the current challenge of re-fitting the wing-body join, the possibility of changes to the electrical and environmental control systems, and simply the poor 787 track record," said Credit Suisse analyst Robert Spingarn.
Boeing hopes to be making 10 of the 787 planes a month by the end of 2013.
Last month, the firm said it already had 850 orders.
It also revealed that it had received 13 new orders for 787s between April and June, but that airlines had cancelled 41 others.
The 787 Dreamliner is a hugely important plane for US-based Boeing in its long standing rivalry with Europe's Airbus.
It was the first unveiled in July 2007 and is the firm's first all-new jet since 1995.
It is designed to make use of carbon fibre to make it much lighter and more fuel efficient than traditional aluminium planes.