It’s time I apologised to all fellow parents … and confess that I tell every graduating class I address that their best wealth-building opportunity is to stay living at home and save, save, save.

“But pay board – it’s great practice managing money and you might even be able to convince your mum and dad, if they can afford it, to stash your cash and return it to you later,” I disloyally divulge.

Because, for parents, the “afford it” bit is the rub. And you can’t have missed last week the rather entertaining story of a US couple who turned to the courts to evict their 30-year old s(p)on(ge).

Well, the collective parental cost of Australia’s stay-at-home adults is now $12.2 billion a year, according to a mozo.com.au survey of 1000 Australians, given exclusively to Fairfax Media. That frighteningly fat figure is calculated from ABS data and the spend reported by parents in this survey.

Almost one in three adults under 35 remain at home, analysis of ABS data indicates. (It’s on the increase too: the 2016 census showed a 20 per cent jump in the number of 25 to 34-year-olds sticking around … to nearly 400,000 across Australia).