While most of us are struggling to regain our net worth after the Great Recession, the richest Americans are preparing to transfer $6 trillion in assets over the next three decades.

According to a new report by global wealth consultancy Wealth-X, $16 trillion of global wealth will be transferred over that time — mostly to family members — and 40% of that, or $6 trillion, will be transferred within the U.S. Of that $16 trillion, $6 trillion will be liquid assets (which can be converted quickly into cash) and philanthropic bequests comprise $300 billion of this upcoming wealth transfer, “The Wealth-X and National Financial Partners Wealth Transfers Report” (pdf) found. Ultra-high net worth individuals who are 80 years old or above are on average five times wealthier than those under 40. “This will be the largest wealth transfer in history from one generation to the next,” says Wealth-X President David Friedman.

And many of those passing on their wealth are self-made individuals. Only 25% of those on the Forbes list of the 400 richest Americans were self-made billionaires in 1984, compared with 43% last year. The wealth of the Forbes 400 has soared 1,832% since 1984, from $125 billion to $2.29 trillion last year. Upper-income Americans have also fared well over the last three decades. The wealth gap between America’s upper-income and middle-income families has reached its highest level on record, according to the Pew Research Center. In 2013, the median wealth of the nation’s upper-income families ($639,400) was nearly 7 times the median wealth of middle-income families ($96,500), the widest wealth gap seen in 30 years.

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Middle-class Americans won’t be so fortunate when it comes to transferring wealth, however. The expectation has been that every generation will do better than the last, but this may not be the case with those who bought homes during the economic boom. All American households since the recovery have started to reduce their ownership of key assets, such as homes, stocks and business equity, according to a recent survey by the Pew Research Center. From 2007 to 2010, the median net worth of American families decreased by 40%, from $135,700 to $82,300. Rapidly plunging house prices and a stock market crash were the immediate contributors to this shellacking.

And upward mobility hasn’t changed much for ordinary Americans. Some 20% of children born in the middle-income distribution reached the top, a figure that hasn’t changed in a decade, according to a report released last year by the National Bureau of Economic Research in Washington, D.C. “Such a large transfer of wealth [among the ultra-wealthy] will exacerbate wealth inequality,” says Signe-Mary McKernan, senior fellow and economist at the Urban Institute, a nonprofit organization that focuses on social and economic policy. “African-American and Hispanic families are about five times less likely than white families to inherit money and when they do inherit money they inherit less than white families.”