The annual cost to the federal budget of the government’s investment in the national broadband network will grow in coming years.

The cost to the budget in 2016-17 is estimated to be about $580m, a report by the Parliamentary Budget Office released on Wednesday shows.

It is tipped to rise to more than $730m in 2019-20 and to $2.1bn by 2026-27.

The PBO said the final cost of the government’s financing of NBN Co wouldn’t be known until it was privatised and the market decided on a value.

Until then, the commonwealth would continue to bear an annual cost.

“If the sale price of NBN Co is less than the commonwealth’s cumulative cost of financing NBN Co, then the NBN would have an enduring cost to the budget,” it said.

