Over half of millennials believe their parents will leave them an inheritance, according to a recent Charles Schwab survey. But they may be disappointed.

The expectation makes sense. Previous generations have passed on significant amounts of money, and when the oldest Baby Boomers started to hit retirement age, experts touted the "great wealth transfer" that would occur, since this generation has an estimated $30 trillion.

Yet only about one in five people actually received any kind of inheritance between 1989 and 2007, Schwab reports.

A survey last year reached a similar conclusion. Nearly 70 percent of millennials in the Natixis U.S. Investor Survey reported that they expect an inheritance, yet only 40 percent of their parents planned to leave one.

A major part of this shift away from inheritances is increasing longevity. People are living longer, they're healthier, so they need to use more of their savings to support themselves, Carrie Schwab-Pomerantz, a financial adviser, board chair and president of the Charles Schwab Foundation, tells CNBC Make It.

"Never consider an inheritance as part of your financial plan. That's dangerous," Schwab-Pomerantz says.