Bill Gates remains in the top spot for the fourth year in a row and has been the richest person in the world for 18 out of the past 23 years.
According to Forbes' 2017 billionaire list, the US President is now only 544th in the global ranking of the world's super-rich.
"Midtown Manhattan real estate is down; therefore, so is Donald Trump's fortune", the business magazine said in a statement.
The Forbes list also revealed that the number of people with assets of more than 1 billion dollars jumped 13% from a year earlier to a record 2,043, largely helped by strong stock prices.
The number of U.S. billionaires on the list was 565, which Forbes attributed to the recent stock market surge since Mr Trump's November 2016 election. Joining Gates in the top three is investor/philanthropist Warren Buffet, with a net worth of $75.6 billion and Amazon CEO Jeff Bezos, the biggest gainer on the list, with a net worth of $72.8 billion.
Trump tumbled more than 100 spots to No. 544 on the magazine's 31st annual list, largely because of the impact of the slumping NY real estate market on his holdings.
It was a different story for the newly minted US President Donald Trump, whose wealth shrunk to $US3.5 billion on the back of a softening NY property market.
At the top is a longtime staple of the Forbes list, Microsoft co-founder Bill Gates, with a net worth of $86 billion.
But not all of the trends were negative for Trump.
The release last week of Trump's budget proposal, which cut United States funding for aid programmes across the world, prompted a rare public rebuke from the Gates Foundation. "Profits are down at Trump Tower, and the overall neighborhood surrounding has been struggling over the previous year".
They have a collective net worth of US$7.67 trillion, up from US$6.48 trillion in 2016, Forbes said.
"There are 11 million people with HIV who are alive today because of the medicines that it provides", Gates wrote. But the list also contained 15 new "self-made" women, mostly from Asian countries, including Vietnam's Nguyen Thi Phuong Thao of budget airline VietJet air.