But the move, announced four months out from the state election, has been branded by some as inadequate.

From July, the seven price brackets that determine how much stamp duty is paid will rise in line with inflation.

NSW Treasurer Dominic Perrottet labelled it the "most significant reform in a generation", noting that the brackets had been largely unchanged since 1986 - when the median house price in Sydney was $100,000.

It's now more than $1 million.

"Whether you are a first homebuyer, a downsizer or upgrading to the family home you will ultimately benefit as a result of this reform," he said in a statement on Monday.

"Pegging stamp duty to CPI will reduce the tax burden on homebuyers allowing them to put more money towards a deposit."

But the NSW Greens said the change made a "mockery" of challenges facing home buyers and renters in Sydney and does nothing to address the issue of housing affordability.

"If the Berijiklian government was serious about housing affordability, it would be capping rent increases to CPI and engaging in genuine property tax reform in NSW," the party's treasury spokesman Justin Field said in a statement.

Stamp duty makes up about a quarter of tax revenue in NSW but is on the decline.

The government collected about $8.7 billion in 2017/18 - $1 billion less than it previously forecast.

It will take $5.5 billion hit over the three years to 2020/21, partly because of new exemptions for first home buyers.

Australian Associated Press