As she draws up plans for a mega-charity, Meghan Markle is following a time-honored tradition among British royals: Go to America. That’s where the money is.

While the stateside branches of charities connected to the British royal family rake in millions every year from Americans enamored with the House of Windsor, they spend heavily on administration and travel and sometimes skimp on the cause, according to a Post review of their federal tax returns.

A Chicago-based charity linked to Queen Elizabeth’s 98-year-old husband, Prince Philip, and specifically set up to help young people in the US, raised more than $600,000 in 2017, but delivered only $45,898 — a little more than 7 percent — to those kids.

The bulk of donations raised by the National Office of the Duke of Edinburgh’s International Award USA was spent on administrative costs, including travel and salaries, its latest available tax filings show. It ended the year $91,524 in the red, tax filings show.

The group’s American CEO attributed the high administrative costs to staff training for the recently created American arm of the charity, which was set up in 2016.

“We’ve had a lot of start-up costs,” Elizabeth Higgins-Beard told The Post. Among the expenditures was $40,741 in travel and $314,326 in salaries and wages, tax filings show.

The charity, which was established by Prince Philip in the UK in 1956, helps youth between the ages of 14 and 24 around the world seek out challenges and connect with community mentors and role models.

Higgins-Beard said that all of the young people who appealed to the US group for help to fund their participation in a series of challenges in 2017 were given financial aid.

The Prince of Wales Foundation, a charity linked to Prince Charles, spent $641,175 on administrative expenses last year, including $297,902 on the salary of its Washington-based executive director and more than $82,000 on lawyers, tax filings show.

The non-profit, with a wide mandate to improve health care, the arts and urban renewal, also spent $69,982 on an office a few blocks north of the White House.

The group raised just over $8.4 million in the US last year, and sent $8,902,142 abroad, mostly in wire transfers, to pet causes like the Royal Drawing School in London and the Dumfries House museum in Scotland, along with unidentified groups in Europe, the Caribbean and Central America, according to its most recent tax filings.

“Travel of celebrities and royals should never be part of a charitable purpose,” said Linda Sugin, an associate dean at Fordham Law School and an expert on non-profits. “I don’t think it’s just a problem of transparency but there seems to me that a lot of private benefit happens with these charities. You can’t use a charity to feed your celebrity.”

Prince Charles’ US charity ended 2018 with a negative balance of more than $1 million.

While all of the groups solicit donations on their websites, some royals have been criticized for other fundraising methods, including selling access at private functions and sporting events.

The American Friends of the Royal Foundation of the Duke and Duchess of Cambridge, under the patronage of Prince William and Kate Middleton, charged $50,000 per couple to attend a private dinner party with William and Kate at the Gramercy Park home of British advertising executive Sir Martin Sorrell and his wife Cristiana in 2014, according to the Daily Mail.

The New York City-based group also charged $84,000 for guests to play polo alongside Prince William in California in 2011, the year the group was founded in Delaware.

The group, which has its offices on Third Avenue, spent $45,000 on an “outside contractor” for an unknown event and $28,673 on travel, according to its 2017 tax filings, the latest available. Another $72,000 went to employee compensation and $14,484 to accounting.

In that year, the charity raked in $740,000 in donations. It donated $100,000 to Home Base, a program for veterans and their families in the US, and spent a total of $522,963 on causes ranging from youth empowerment to environmental conservation.

Calls to the American Friends of the Royal Foundation went unreturned last week.

Prince Harry, who was a patron of the Royal Foundation for years, split with his brother and sister-in-law’s group earlier this year. He and his wife, Markle, set up a separate charity — the Sussex Royal Foundation of the Duke and Duchess of Sussex — in London in July, public records show. A spokesman did not return messages seeking comment.

Royal Charities in the USA in the USA

With Prince Harry and Meghan Markle working to establish a foundation of their own, perhaps they can learn from the nonprofits run by their royal family members — where money raised for charity doesn’t necessarily end up in the hands of those who need it.

Prince Philip | National Office of the Duke of Edinburgh’s International Award USA

$600,789 total worth

$636,866 raised in 2017

$445,891 spent on salaries

$40,741 on travel

$45,898 given to kids

Prince William and Kate Middleton | American Friends of the Foundation of the Duke and Duchess of Cambridge

$499,582 total worth

$743,913 raised in 2017

$192,539 spent on administrative expenses

$72,000 in salaries

$45,000 on contractor

Prince Charles | The Prince of Wales Foundation