US president Donald Trump’s fortune has fallen by about $1bn to $3.5bn over the past year, as measured by Forbes magazine in its annual list of the world’s billionaires.

However, overall it has been a good 12 months for the world’s wealthiest individuals, with a record 233 moving into the billionaire bracket, taking the global number of people with nine-zero fortunes to 2,043 – the most ever, according to Forbes.

The billionaires in Forbes’ list are worth a combined $7.67tn (£6.18tn) – more than twice the UK’s annual gross domestic product (GDP).

Kerry Dolan, co-editor of the Forbes billionaires list, published on Monday, said the gains are mostly the result of booming stock markets and the rising price of oil over the past 12 months.

Global markets have hit record highs due to the so-called “Trump bump” following the election of Donald Trump as US president, with the Dow Jones soaring above 20,000 points for the first time ever and the UK’s FTSE 100 closing at a record 7,415 points last week.

The fall in Trump’s net worth is due to a drop in the value of office space in Midtown Manhattan, where the president owns about 10 buildings. Forbes said Trump had fallen from the world’s 324th-richest person to 544th.

Trump has refused to publish his tax return to show the true scale of his wealth but during the campaign he claimed he was worth “in excess of $10bn”.

Dolan said that in previous years the real estate tycoon has personally challenged Forbes for underestimating his fortune. “We contact everyone we can to give them the opportunity for feedback. Over the last 31 years we have been compiling this list Trump has given us a lot of feedback, believe me, ‘You guys are too low I am worth far more than you say’,” she said. “He didn’t call back to dispute our estimate. I would hope that running the country is more important to him right now than Forbes’s value of his net worth.”

The richest person in the world remains Microsoft founder Bill Gates, who saw his fortune grow by $11bn to $86bn. He is followed by investor Warren Buffett, and Amazon founder Jeff Bezos, who was this year’s biggest gainer with a $27.6bn increase in his fortune to $72.8bn.

The US accounts for the biggest population of billionaires with 565, an increase of 25 on last year. But China is catching up with 319 billionaires, and a further 68 if Hong Kong and Macau are included. Germany is third with 114 billionaires.

The number of UK billionaires increased from 50 to 54, with new entrants including Philip Day, the man behind Edinburgh Woollen Mill, and Simon Nixon, the co-founder of

The richest people in the UK are the Hinduja family, who control a conglomerate of businesses including cars and banks, who are worth $15.4bn. Property and internet investors David and Simon Reuben come second with a $15.3bn fortune. The third richest, and among the biggest gainer, is Jim Ratcliffe the founder and chairman of chemicals group Ineos.

Among the biggest British losers is Sports Direct founder Mike Ashley whose fortune dropped by 25% to $2.6bn. His wealth, which is largely held in Sports Direct shares, has roughly halved over the past two years as shares collapsed following the Guardian exposé of “Victorian workhouse”-like conditions in its distribution warehouses.

“His [Ashley’s] wealth has fallen by roughly half, but I’m sure on a day-to-day basis his quality of life hasn’t changed that much,” Dolan said.

Sir Philip Green and his wife, Tina, the owners of Arcadia, which owns Topshop and once owned BHS, also lost just over $1bn, with their fortune slumping to $4.8bn. They fell more than 100 places in the rich league table to 339th.