Millions more will be spent on the final stage of the Centrelink payments system overhaul.

Last week’s budget papers included $539.6 million over four years for Services Australia, including $166.9 million to complete the welfare payment infrastructure transformation (WPIT) program.

The money should see Services Australia improve on earlier changes to the distribution of disability, carers and families payments as well as the age pension.

The agency is also working on a new entitlements calculation engine, in order to decommission the legacy income security integrated system (ISIS).

A recent audit found delays to the decommissioning of ISIS have “put at risk one of the original objects of the WPIT program and negated realisation of all the expected benefits”.

The government says it expects to “achieve savings of $317.4 million over four years from 2020-21” because of the improvements.