Parents could end up $227,000 richer if they accept one hard truth

Most parents are footing the bill for at least some of their adult kid's expenses, and it could be costing them hundreds of thousands of dollars, a recent NerdWallet report finds.

"On average, a parent covering a child's living expenses for five years and borrowing money for college tuition is missing out on $227,000 — almost a quarter of a million dollars — in retirement savings," NerdWallet reports. "A higher cost of living or supporting multiple adult children could drive that number even higher."

The site also found that 80 percent of parents of adult kids "are covering, or have covered, at least a portion of their adult children's expenses after they turned 18."

Parents who are covering college tuition or student loans could be missing out on nearly $80,000 in retirement savings, NerdWallet reports: "The average parent takes out $21,000 in loans for their child's college education, but the hit to retirement savings is almost quadruple that amount." That's because of the power of compound interest, which causes your wealth to snowball over time.

"As parents, we tend to want to do everything we can to help our children succeed," says Andrea Coombes, NerdWallet's investing expert. "But sometimes we focus on the present at the expense of the future. … Put your own retirement savings plan front and center right now."

Think about it this way: If you don't set aside enough money for retirement, your child may have to support you in the future, which could end up being more expensive than student loans.

As certified financial planner Lazetta Braxton told CNBC: "I drive parents to think of themselves first — it's the greatest gift they can give their kids. Because there's no guarantee the kids will take care of them financially or otherwise in their old age."

At the end of the day, the decision of whether or not to support your adult kid is highly personal. And saving enough for retirement while helping them out financially is more than possible, especially if you start socking away money years in advance.

But if you're behind on your retirement savings, you may want to rethink covering your adult kids' bills — or at least be aware of how much it's costing you.

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