The federal government delivered on its $20.5 billion pledge to rebuild lower Manhattan after the 9/11 terrorist attacks, according to the city’s Independent Budget Office.

“We got what we were promised,” said IBO spokesman Doug Turketsky.

Former President George W. Bush made the promise shortly after 9/11.

The largest share of the federal money, $4.6 billion, went to transportation projects, such as the Fulton Street Transit Center, which will link 11 subway lines.

The center, which is currently under construction, will cost an estimated $1.4 billion — nearly double the originally budgeted $799 million.

Of the $8 billion in triple tax-free Liberty Bonds authorized for redevelopment, only $700 million remain. Officials said they expect those dollars will be used before the December 2012 deadline.

The one federal allocation that remains largely untapped is $2.9 billion in tax breaks offered to a limited number of businesses that hire new employees and bought new equipment. That benefit expired in 2004, the IBO said.