NEW YORK -- U.S. President Donald Trump's ranking in the Forbes list of wealthiest Americans has dropped, as the magazine said the value of some of his Manhattan real estate holdings has declined recently.

Forbes ranked the first billionaire president as the 248th-wealthiest person in America and put his wealth at $3.1 billion . The year before, he was ranked 156th and Forbes said he was worth $3.7 billion.

As a candidate, Trump said his net worth was more than $10 billion, but Forbes pegged that figure at $4.5 billion in September 2015. By Forbes' estimates, Trump's wealth has fallen 31 per cent in two years.

According to Forbes, half of Trump's wealth comes from New York City real estate. It says the value of luxury real estate is down, especially around Fifth Avenue. That sharply reduced the value of Trump Tower and other properties Trump owns or has stakes in.

Forbes also said some of Trump's golf properties declined in value and that he spent $66 million on the presidential campaign as well as $25 million to settle a fraud lawsuit brought by former students in his defunct Trump University program for real estate investors.

Forbes' list is once again topped by Microsoft co-founder Bill Gates with a net worth of $89 billion, followed by Amazon's Jeff Bezos and Berkshire Hathaway's Warren Buffett.