NBN Co chief executive Bill Morrow says things are going well, despite needing a special loan from the Federal Government late last year.

A $19.5 billion top-up was granted last year, on top of the government's $29.5 billion capped contribution.

The extra money was negotiated on commercial terms, despite original expectations that the private sector would cover any shortfall in the NBN's budget.

But Bill Morrow has doused questions about the private sector's confidence.

He says he is confident the money could have been raised from the private sector.

“We did not actually tap into the banks to start the process but the government stepped in and said they would loan it to us rather than have us go to that market,” Mr Morrow said.

“We're pleased with that because it made our life much simpler to secure those funds.”

Mr Morrow refused the classification of the $19.5 billion government loan as a “rescue”.

“No it wasn't a rescue at all. It was clearly just prudency and managing taxpayers money than leaving it to us to go to the external markets,” Mr Morrow said.

Mr Morrow said he understood concerns about the final sale price of the NBN.

Consultants at KMPG estimate the NBN may have to be written-down in value by as much as $25 billion to attract private interest.

“It is the biggest [project] that the country has seen. There is a lot of money involved so it's natural to be sceptical and to be concerned,” Mr Morrow said.

“There's a lot of people that will speculate about what the value is and what will happen if it ever does come to selling. I think we should worry about that when the time comes.”