14/12/2016 12:17 PM AEDT | Updated 14/12/2016 2:59 PM AEDT

The NBN Just Got That Little Bit More Expensive, Again

To the tune of $8.8 billion.

NBN fibre optic cable rollout.

SYDNEY -- It's nowhere near finished yet but the cost to government -- and therefore taxpayers -- of the National Broadband Network (NBN) has blown out by another$ 8.8 billion, mainly thanks to public debt interest payments.

And the Parliamentary Budget office (PBO), which has looked at the NBN's impact on the federal budget, has predicted the public cost will rise until the NBN is privatised and the market sets a price on the NBN.

The PBO states the current NBN cost estimate for an Australian rollout by 2020 is $49 billion and the Government's NBN investment (equity funding and loans) to date is $20.3 billion (at June 30) out of its $29.5 billion in equity funding. As well there is a recent $19.5 billion government loan to finish the NBN rollout.

But the PBO has found the Government's investment in NBN Co has seen the Commonwealth's net worth drop by $8.8 billion, due to public debt interest (PDI) payments, NBN Co's accumulative losses and a $1 billion asset revaluation stemming from "the early years of the rollout of the NBN".

The PBO also finds the government's investment in the NBN has cost $580 million each year for the past two years which is estimated to rise to $730 million in 2019-20 and $2.1 billion by 2026-27.

The PBO said the final NBN costs to government will not be known until NBN Co is privatised and the market sets a price on the NBN.