Twenty-four flood-affected homes have been bought by Brisbane City Council in 2011-12 under its flood buy-back scheme, eight fewer than predicted.

The council had expected to buy 36 properties, with 13 homes on the buy-back list before the January 2011 flood.

It has been revealed $1.2 million the $10 million set aside in last year's council budget to buy flood-affected homes remained unspent.

A spokesman for lord mayor Graham Quirk said one further flooded home was under negotiation and should also be acquired by the end of the month.

The number of homes flooded in the January 2011 floods and earlier creek flooding was revealed after close questioning by opposition Labor councillors of the council's March quarter financial position.

Cr Quirk said the complete $10 million would be spent by June 30.

"The reality is that we will be spending all of that money on voluntary home purchases," he said.

"Of the 36 listed, the reason we have people receiving letters saying we can do no more this financial year is because we are committed.

"We are going through the process of settlements in relation to this program.

"Remember this is a voluntary program, there has to be an agreed price between the resident and this council."

Labor councillor Steve Griffiths, whose Moorooka ward was badly flooded last year, said the voluntary home purchases should have been completed by this month.

"We are still finding excuses to carry this money over," he said.

"It is disappointing."

Cr Griffiths said he also believed the council was "fudging the figures".

"I think a lot of this money will be re-launched in the lord mayor's upcoming budget," he said.

The council's voluntary home purchase scheme began in 2006, after then-lord mayor Campbell Newman completed the suburban flood taskforce in August 2005.