American parents are eating into their retirement fund by spending billions on supporting their adult children, research suggests.

A recent study from Merrill Lynch found that 79 per cent of parents continue to serve as the 'family bank' for their grown-up children.

They pay for big-ticket items like college and weddings but also for everyday expenses.

Parents of adult children contribute $500billion annually, twice the amount that they invest in their own retirement accounts.

American parents are spending billions on supporting their adult children financially by paying for college education and weddings

Sixty-three percent of parents said in the study they have sacrificed their financial security for the sake of their children.

Figures from the US Census Bureau show 34.1 per cent of people aged 18 to 34 lived under their parents' roof in 2015. The figure has increased from from 26 per cent in 2005.

One in four young people living in their parents' home neither go to school nor work.

According to the U.S. Census Bureau, 34.1 percent of people aged 18 to 34 lived under their parents' roof in 2015. That's up from 26 percent in 2005

Lorna Sabbia, head of Retirement and Personal Wealth Solutions at Bank of America Merrill Lynch, claimed parents may chip into their own retirement fund by supporting their children.

'If you get to a point where truly your retirement savings or savings just in general is completely depleted to support your kids, ultimately your kids may actually have to provide financial support for you later on in life as well,' she said.

Denver tax and estate planning attorney Denise Hoffman White suggesting that supporting adult children may harm them in the long run.

Sandy (left) and Gary right) Cooper try to teach their children to make sensible life choices

Sandy and Gary Cooper, pictured with their children, hopes teaching them good life lessons will fortify their children in the future

'You start to see adult children who are not being put in a position where they can be successful in their own right because they have a crutch which is different than an opportunity,' said White.

White tries to train clients who are parents to talk to their kids about money the same way they teach manners or good grades.

Gary Cooper, a private wealth adviser at UBS Financial Services, tries to teach his children to make sensible life choices with his wife Sandy.

He told CBS: 'You want to give … but sometimes giving them isn't actually helping them. Our job is to help them, not do for them, right?

'It's a concept of saving, of budgeting, of understanding -- that feeling of delayed gratification'.

Sandy Cooper hopes these lessons will fortify her children for the future.

'So I think they'll have the intrinsic pride and motivation to deal with anything that gets thrown their way,' she said.

Raising financially independent kids these days may be about teaching an old-fashioned lesson: earn before you spend.