CoreLogic says Sydney real estate prices are likely to have remained flat in August, or even post a modest decline.

The figures were released at CoreLogic's launch of changes to the way it calculates its hedonic home price index.

Head of research, Tim Lawless, said tighter lending rules were hurting Sydney real estate the most, because Sydney has the highest percentage of investor-owned property.

"Sydney has been gradually cooling since November last year, auction clearance rates have starting slowing... all signs the market is cooling," he said.

Changes to CoreLogic's hedonic home price index

CoreLogic announced changes to the way it calculates its hedonic house price index. The changes will take effect from 1 September.

Sampling will be improved, off-the-plan sales will be calculated differently, and improved geographic boundaries and better modelling will be used. Data for the new index will go back to 1980.

The new index will deliver less volatile readings, and will result in slight changes to growth figures.

For the year to the end of July, the old index showed Sydney prices rose 12.4 per cent for the year to July 2017, while the new index shows a gain of 15.7 per cent.

In Melbourne, the old index showed a rise of 15.9 per cent for the year to July 2017, while the new index shows a rise of 13.0 per cent.

Click here to read more about the changes CoreLogic is making to its Hedonic Home Value Index.

Read more about Sydney and Melbourne real estate:

Why is Melbourne's property market outpacing Sydney's?

Chinese national Qi Yang confirmed as buyer of Melbourne's $40m Toorak mansion

Melbourne - is it really the world's most liveable city?