Survivors of abuse will likely have to wait longer to read the report of the Royal Commission into Abuse in Care.
The high-level inquiry into abuse that occurred in state and faith-based care was due to hand in its report on 28 March.
Department of Internal Affairs secretary Paul James said his agency intended to ask for a third extension, when presenting to MPs on Monday morning.
James said he had been responsible for providing administrative support for five Royal Commissions and "never managed to deliver one on time and on budget".
"They are very complex and often put together under a real point of pressure; something's happened or there is an issue that needs the highest possible level of scrutiny outside of the court system."
He cited the significant scale of the Abuse in Care inquiry and a legal hurdle were making it hard to meet the target date.
"There has been a live legal challenge, a judicial review, running in respect of that Royal Commission of Inquiry into Abuse at the moment," James said.
"Some of those things make it hard to hit the reporting deadlines or stated budget."
Inquiry chairperson Coral Shaw has previously said the scale of abuse is beyond what anyone had ever imagined at the start of the inquiry.