Parenting has no specific end date. Sure, technically, you're no longer legal responsibility to support your children after they turn 18, but in general, people don't cut their kids off financially when that birthday rolls around.

So some parents help pay for college. Others let their kids live with them for years after they reach legal adulthood. The trend of moving back home for a time after college is well established -- as recently as 2016, the Pew Research Center found nearly a third of 18 to 34 year olds were living with their parents. And even those with their own homes or apartments may be getting financial support. For a large number of expense categories, millennials on average figure that mom and dad should be covering the bills for a year or so longer than their boomer parents think is reasonable.

All that parental help can plant a major detour along parents' road to retirement. Among respondents to a new Bankrate.com survey, fully half of those who had adult children said that financially supporting their grown offspring had hindered their ability to save for retirement. And roughly 1 in 6 (17%) said that the impact was significant.

Supporting your own grown kids could keep you from retiring. Image source: Getty Images.

Who is this hurting?

People want their kids to succeed, and in many cases, they define that as having a lifestyle that at least approximates the one the parents enjoy. That may explain why higher earners are more likely to sacrifice their own nest eggs to help adult children (while lower earners are more likely to not be saving for retirement at all).

Among families with household incomes of at least $80,000 a year, 60% of parents said that they'd hurt their own retirement savings in order to help adult children pay bills. And while fewer families making less than $50,000 a year are paying bills for grown kids, 17% of them have yet to save anything for retirement.

"Addressing the financial elephant in the room isn't always an easy conversation to have, but it is imperative for your future and your child's long-term success," said Bankrate analyst Kelly Anne Smith in a press release. "By not prioritizing your own expenses and retirement savings, that is when everyone suffers."

Make the tough choices

Helping your offspring financially means more than just shelling out cash -- it's also about teaching them how to make smart money choices that fit within their budgets. This education should start young. So parents could consider involving their children in certain financial decisions. For example, give the kids a vote in whether to take a week-long resort vacation, or to instead buy annual passes to the local theme park and get a new video game console. But make it clear why "both" is not an option.

As kids get older, it's possible to involve them in bigger decisions and strategies, such as how their college educations will paid for. If mom and dad could in theory afford to swing the lion's share of the bill at a pricey private institution -- but at the cost of their financial stability in retirement -- the child needs to understand the ramifications.

That may lead your child to a decision to pick a public university, spend a year or two at a community college, or take on more loans to themselves. Just recognize that they can't make informed choices without understanding the full picture.

"Setting clear boundaries and creating a game plan for your children are a couple ways to wean them off your wallet, so you can focus on your future financial security and they can learn to be financially independent," said Smith.

Of course, not every child chooses what's best for the entire family, and not every financial decision is planned. An unexpected medical emergency may, for example, put a parent in a position where paying the bills for their adult offspring doesn't really feel like a choice.

Regardless, if you're the sort of parent whose first instinct when your grown children's desires outpace their budgets is to reach for your checkbook (or worse, your credit card), try to remember that it's OK to say no. You should be placing your own long-term needs ahead of their short-term wants. And as hard as that many be to do, it's a lot easier if you start talking openly about money with them early.