Boomer and Gen X parents may be harming themselves — and their adult children — by spending far too much money supporting financially struggling millennials, according to a 2018 study by Merrill Lynch in partnership with Age Wave, a thought leader on aging.

“We estimate that parents of adult children annually spend $500 billion on them — twice what they contribute to their own retirement accounts,” said the study report, “The Financial Journey of Modern Parenting: Joy, Complexity and Sacrifice.”

The startling $500 billion figure includes full or partial support for adult children’s expense categories, including food or groceries (60 percent), cellphone (54 percent), car (47 percent), school (44 percent), vacations (44 percent), rent or mortgage (36 percent), and student loans (27 percent).

The $500 billion parents spend supporting these adult children under the age of 34 does not include less frequent but big-ticket items such as weddings and the first homes.

Nearly one in three temporarily independent young adults between the ages 18 and 34 returns to live in their parents’ homes. The surprising figure represents a 50 percent increase in the number of “boomeranging” adult children in 1960, according to the Census Bureau.

Drawing upon the “family bank,” the study indicates, is not limited to adult children who refill their parents’ formerly empty nests.

It’s the norm, in fact.

Kantar TNS, a market research and information group, gathered data from more than 2,500 U.S. respondents — and found that nearly 80 percent of parents provide some type of financial support to their adult children.

“Compared to all I’m spending on my two adult children’s upkeep, having them boomerang back and live at home would be relatively inexpensive,” said one focus group participant who was quoted in the report.

The startling $500 billion figure includes full or partial support for adult children’s expense categories, including food or groceries (60 percent), cellphone (54 percent), car (47 percent), school (44 percent), vacations (44 percent), rent or mortgage (36 percent), and student loans (27 percent).

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The long-term financial sacrifices made by parents to support their adult children are substantial. One in four of the parents surveyed said they are willing to take on debt and pull money from a retirement account to make these financial contributions.

Half would pull from their savings.

These sacrifices, made from a heartfelt desire to be generous and supportive, can ultimately backfire in ways neither the parents nor their adult kids would suspect.

Related: The Secrets of Raising Financially Savvy Children

The study authors caution parents to consider the possibility that funding their young adult children’s expenses now, by drawing on retirement savings, may result in becoming financially reliant on those same children down the road.

So what’s a loving parent to do? Are today’s parents handicapping both themselves and their children with too-generous contributions, such as those made for cellphones, vacations and cars?

Share your thoughts in the comments section below.

Michele Blood is a Flemington, New Jersey-based freelance writer and a regular contributor to LifeZette.