Lord Mayor of Brisbane Adrian Schrinner says he is expecting a cost increase of 11 per cent on key city infrastructure projects when a new budget is handed down next week. 

Inflationary pressures caused by the COVID-19 pandemic, February's floods and other global factors have contributed to the $400 million price hike over the next three years.

Cr Schrinner said the changes meant the council's $337 million surplus would be eaten away by $57.7 million.

In June, the council delivered a rates increase of nearly 5 per cent, the city's highest increase in more than a decade.

The council's net debt grew to $3 billion, up from $2.8 billion, and it faced a $330 million flood recovery bill, plus $220 million of revenue loss from the previous two years of the pandemic.

Cr Schrinner said the "significant cost increases" would be finalised by next week.

He said the money put aside for a "rainy day" was now needed.

"But even with these impacts we will retain a balanced budget.

"We're not taking the foot off the accelerator when it comes to Brisbane Metro, green bridges, all the investment we're making right across the city. 

"Our city needs it, we're going to pursue it."

'Paying more and getting less'

But Labor Opposition leader Jared Cassidy said next week's budget review would "remind long-suffering rate payers they are paying more and getting less".

He said this year's budget had delivered the "highest rate increase in a decade and [the] highest debt".

"The Brisbane Metro project has blown out from $944 m to $1.7b, but [is] delivering less than was initially promised," Cr Cassidy said.

"Anything could be cut from the suburban works schedule without anyone knowing."