The largest intergenerational transfer of wealth in U.S. history is expected to shift trillions of dollars to Generation X and millennial heirs over the next two decades, but most of the money will go to families that are already among the nation's wealthiest, according to a new analysis, The Washington Post reported Wednesday.

Visa Business and Economic Insights estimates baby boomers will transfer about $36 trillion in wealth to their heirs over the next 20 years, with nearly three-quarters of recipient households already ranking among the country's wealthiest when they inherit the money.

The findings suggest the "Great Wealth Transfer" will reinforce current wealth disparities while providing only a modest boost to consumer spending, as much of the inherited money is expected to be invested rather than spent.

Baby boomers, born between 1946 and 1964, hold some $93 trillion in assets, according to Visa. After accounting for retirement spending, taxes, and liabilities such as mortgages, roughly $36 trillion is expected to remain available for inheritance.

That equates to an average inheritance of about $515,000 per household, although the payouts will be heavily concentrated among wealthier families.

"The richest boomers have the most to give away," Visa found, estimating that households in the 90th to 99th percentiles of wealth control $44 trillion in assets, compared with $16 trillion held by the bottom 90% of boomer households.

Because affluent parents are more likely to leave substantial estates, their heirs also tend to be financially secure, meaning much of the transferred wealth is expected to remain in investment portfolios instead of flowing into the broader economy.

"Wealthier Americans are going to be putting that money into the stock market or real estate," said Jeremy Ney, a professor at Columbia University's business school and author of the American Inequality newsletter. "It doesn't buy groceries or cars, it just changes your accountant's week."

Visa estimates that only about $8 trillion, or 8.6% of boomers' current assets, will ultimately be spent into the economy after being inherited.

While that spending is expected to provide an economic lift, its impact will be limited. Visa projects the inherited wealth will increase annual consumer spending growth over the next two decades from about 2% to 2.1%, with much of the added spending directed toward housing, automobiles, travel, and retail purchases.

"Eight trillion dollars is nothing to sneeze at," said Visa Chief Economist Wayne Best, noting that the amount available for spending is significantly smaller than the total wealth held by boomers after accounting for taxes, retirement expenses, and debt.

Longer life expectancies are also shaping who benefits from the wealth transfer, economists said.

Jonathan Parker, professor of financial economics and co-director of the MIT Sloan Consumer Finance Initiative, said many heirs will inherit assets later in life than previous generations, often after they have already accumulated significant wealth of their own.

"There's tax incentive reasons to wait until you pass away to pass along those bequests," Parker said.

At the same time, some boomers are choosing to distribute portions of their wealth before death. Visa found increasing numbers are helping children buy homes or pay for family vacations with grandchildren while they are still alive.

The report excluded the wealth of the richest 1% of baby boomers, whose estates are more likely to be directed toward charitable foundations or other private purposes than to typical household heirs.

"They don't really spend like the rest of us," Best said.