According to Forbes magazine, Donald Trump’s fortune dropped $800 million in one year.

The business magazine now estimates Donald Trump’s net worth at $3.7 billion.

Forbes said the decrease was mainly due to the “softening” of the New York property market.

Donald Trump, who once wrote a book called Midas Touch, has said the country needs a dealmaker-in-chief in the White House.

During September 26 presidential debate, he said: “I have a tremendous income … it’s about time that this country had somebody running it that has an idea about money.”

Image source U.S. Marine Corps

The magazine, which has been counting Donald Trump’s wealth for more than three decades, cites the decline of the New York retail and office real estate market for the slump in his wealth.

Of the 28 buildings that Forbes assessed, 18 declined in value, including his flagship Trump Tower on Manhattan’s Fifth Avenue.

Donald Trump’s property at 40 Wall Street and Mar-a-Lago, his private club in Palm Beach, Florida, also lost value, according to Forbes.

However, seven Trump properties, including San Francisco’s second-tallest tallest building, increased in value.

A central tenet of Donald Trump’s candidacy has been that his ability to fund his own White House run meant he was not beholden – like his rivals – to major donors.

The Republican has invested about $50 million of his own money so far in his presidential bid, but has clawed some of that back by, for example, locating his offices in Trump Tower and billing his campaign for rent.

Forbes estimates Donald Trump’s controversial remarks about Mexican immigrants during his campaign launch cost him about another $100 million in lost deals with NBC Universal, Univision and Macy’s, among others.

When Donald Trump filed his financial disclosure with the Federal Election Commission this year his campaign said he was worth “in excess of TEN BILLION DOLLARS”.

However, Forbes says he is worth $3.7 billion, Bloomberg puts it at $3 billion and Fortune says it’s $3.9 billion.

One reason for the discrepancy is that Donald Trump counts the value of his brand – by his own estimate worth some $3.3 billion.

Critics also accuse the billionaire of routinely overstating his income by conflating business revenue and income.

Donald Trump’s refusal to disclose his tax return has fuelled speculation that his bank balance is not as huge as he claims, or that perhaps he’s not paying his fair share of taxes.

Democratic candidate Hillary Clinton suggested at the first presidential debate that the return may reveal “something really important, even terrible, that he’s trying to hide”.

Even if Donald Trump did release his tax returns tomorrow, they would be unlikely to give a true sense of his real wealth.

Tax returns report income and taxes paid on that income, but would not provide a full picture of the value of his assets or Donald Trump’s debt.