The number of workers compared to people aged 65 and over in NSW is set to halve within 40 years, according to new state government projections highlighting the challenge of an ageing population.

The NSW Intergenerational Report, to be released by Treasurer Gladys Berejiklian on Thursday, will provide demographic and other projections for the state to 2056 before the NSW state budget on June 21.

It is published every five years in accordance with the requirement for the government to assess the "long-term fiscal gap" due to an ageing population and other trends.

In a key finding, this year's report will say the ratio of workers to those aged 65 and over will shrink from the current 4:1 to a projected 2:1 by 2056.