Soaring Microsoft shares boosted Bill Gates's fortune by $15.8bn in 2013

Gates, who regained world's richest man title from Mexican telecoms magnate Carlos Slim in May, now has $78.5bn

Less than a quarter of Bill Gates' wealth is held in Microsoft shares – but he is still the largest individual shareholder. Photograph: Getty

The 300 richest people on the planet are $524bn (£319bn) better off than this time last year, with the world's richest man, Microsoft founderBill Gates, increasing his fortune by $15.8bn to $78.5bn over 2013.

Research by Bloomberg's Billionaires Index showed that the world's 300 richest are now collectively worth $3.7tn – more than one and a half times Britain's GDP.

Gates, who regained the title of the world's richest man in May from Mexican telecoms magnate Carlos Slim, made most of his gains from the 40% increase in the price of Microsoft shares. He owns about 4.5% of the company he founded in 1975 and is still the largest individual shareholder.

He also benefited from rallies in other stocks in his portfolio, including Canadian National Railway company (up 34%) and hand sanitiser company Ecolab (up 45%). America's S&P 500 index last year made its biggest gains since 1997.

Gates holds stakes in about 35 public-listed companies and many private firms, including Four Season Hotels, via investment company Cascade Investments. Less than a quarter of his wealth is held in Microsoft shares. He has donated $28bn to the Bill & Melinda Gates Foundation, which is trying to eradicate polio, malaria and measles.

The second biggest gainer in 2013 was Sheldon Adelson, the founder of Las Vegas Sands, the world's largest casino company. His fortune grew by $14.4bn following a 71% rise in the company's share price. Despite its name, most of the company's growth came from the tiny Chinese city of Macau, where casinos collected $45bn in gambling revenues last year – about seven times as much as in Sin City – according to estimates.

Only 70 of the 300 on the list made a loss last year. The biggest was Eike Batista, who has plummeted from being ranked the world's eighth richest man in March 2012 to having a "negative net worth", according to Bloomberg.

Eike, a Brazilian who had made $30bn from oil and gas exploration, lost it all when his company, Oleo e Gas Participacoes, filed for bankruptcy protection in October. Four years ago he had boasted to Forbes magazine that he would become the world's richest man.

Slim was also one of the biggest losers, with his net worth dropping $1.4bn in the course of last year after Mexico's government tried to reduce the dominance of his América Móvil mobile phone company.

More than 100 billionaires were created in 2013, including the youngest female billionaire, Lynsi Torres, the 31-year-old owner and president of US burger chain In-N-Out.

• The headline and subheading on this article were amended on Friday 3 January 2014 to make it clear that Bill Gates regained the title of world's richest man in May last year.