The New South Wales government is laying the groundwork for its stamp duty reforms, despite not yet introducing legislation to parliament.

An online calculator has been set up through Service NSW for prospective first home buyers to work out the difference between paying stamp duty up-front or an annual land tax.

Under the government's proposed scheme, first home buyers can choose either option if they are purchasing a property up to the value of $1.5 million.

"Choice is at the heart of these game-changing reforms that will put keys in the hands of new home owners much sooner," Premier Dominic Perrottet said.

The rate for land tax is set to $400 plus 0.3 per cent of land value.

Treasurer Matt Kean announced the change in the June budget and will unveil the calculator on Monday.

The government is expected to introduce the legislation this week, but it won't have a smooth passage through parliament.

Labor has announced it will oppose the legislation and has previously urged the government to take the policy to next year's March election.

The stamp duty reforms featuring in the election campaign is looking increasingly likely due to the few sitting weeks before the parliamentary term expires to pass the legislation.

The bill could also be examined by an upper house committee before it goes before the Legislative Council, which could further delay a final vote.

The Greens are supportive of transitioning from stamp duty to a land tax, but won't commit to voting for the legislation until the details are revealed.

The Shooters, Fishers and Farmers party are set to oppose it.

Mr Perrottet has pledged to abolish stamp duty since he was the treasurer and the proposed reforms are a scaled back version of what he had previously wanted to achieve.

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