For many Americans, the biggest thing standing between them and a secure retirement is their children. Today, about 50% of Americans are sacrificing saving for retirement to support financially struggling adult children.  

A new study from Bankrate.com reveals at what point parents think they should stop paying for things like mobile phone plans, car payments and student loans for their adult children. The results of this study could help you set financial boundaries with your own grown-up, but still dependent, children.

Risking retirement to finance adult children is the rule, not the exception. The Bankrate study polled 2,553 adults across five age groups: Generation Z (18-22), Millennials (23-38), Generation X (39-54), baby boomers (55-73) and the Silent Generation (74+). An average of one out of two among both Generation X and baby boomers said they were sacrificing or had sacrificed their retirements to help their adult children financially either “somewhat” or “a lot.”

Most don’t expect financial independence to start at 18. Participants were asked when it would be appropriate for parents to stop paying for their adult children across nine categories of expenditures. Those categories included expenses such as car payments, auto insurance, subscription services (such as cable TV or Netflix), credit card bills and travel costs. And though age 18 has long been a standard benchmark for adulthood, only the baby boomer respondents said, on average, that 18 is the age at which children should be paying their own way for any of the categories. And the baby boomers said that this was the appropriate age for financial independence in only a single category—cell phone bills. So, if you have a 19- or 20-year-old child—or even an older one—who is still getting a bit of monetary assistance from you, keep in mind that’s par for the course.

In most cases, 20 is the magic number. Five of the nine categories received an average response of age 20 as the cutoff. Older respondents tended to feel that parents should cut off their children a year or two earlier than younger respondents do, which is not surprising. The one exception to this was subscription services, which got an average answer of age 20 from all five age groups.

Older adult children get more slack on big-ticket items. Respondents across all five age groups were much more lenient when it came to the big, relentless, must-pay bills that can dog a person for decades. The average response was that parents should help their grown children with housing costs until age 21. For both health insurance and student loans, however, the average was 23. In fact, in none of the five age groups was the average response less than 21 as the right age to cut the cord across all five spending categories.

The bottom line, according to Bankrate analyst Kelly Anne Smith, is that when it comes to children, parents need to work on “setting clear boundaries and creating a game plan…so you can focus on your future financial security and they can learn to be financially independent.”