The population of the super wealthy, or those worth $100 million or more, doubled over the past 20 years as asset prices soared around the world, according to a new report.

There are now 28,420 so-called centi-millionaires worldwide, up 12% over last year and more than twice the number in 2003, according to a new report from Henley & Partners, the wealth and migration advisory firm, which used data from New World Wealth.

The surge in centi-millionaires reflects the rapid rise in asset values fueled by low interest rates, which boosted the values of everything from real-estate and land, to stocks, private companies and art. The rise of tech wealth, especially in the U.S., has also helped fueled the growth in the super-wealthy. The number of billionaires in the world has skyrocketed from under 500 in 2003 to more than 2,600 today, according to Forbes and other wealth-tracking firms.

Low interest rates and the resulting flood of money throughout the world since the 2008 financial crisis has also made the money effectively worth less, which has added to the growth of centi-millionaires in terms of dollars.

“The value of money has declined, so in dollar terms, you would expect more centi-millionaires,” said Andrew Amoils, head of research at New World Wealth. “It’s also been fueled by strong growth in the U.S. and Asia.”

Amoils said most of today’s centi-millionaires made their fortunes by starting their own companies or helping to fund startups. The U.S. is still the dominant capital of entrepreneurship and centi-millionaires, with 38% of the global population of people worth $100 million or more, according to the report.

With the era of ultra-low interest rates gone for now, the growth rate for centi-millionaires may slow. The report projects the centi-millionaire population will increase by 38% over the next decade, from 28,420 to about 39,000 by 2033.

“It does look like the next 10 years will be slower than the past 10 years,” Amoils said.

Although the media tends to focus more on billionaires, the report said centi-millionaires are more representative of the world’s super wealthy. The dollar threshold for what it means to be “super-wealthy” has increased rapidly over time, said Juerg Steffen, CEO of Henley & Partners.

“Not long ago, in the late 1990s, $30 million was considered by most banks as the fortune that was needed to meet this status,” he said. “However, asset prices have risen significantly since then, making $100 million the new benchmark.”

While many smaller, less-developed countries have very few billionaires, they may have dozens or even hundreds of centi-millionaires. Amoils said that there is often little visible difference in lifestyle between a person worth $100 million and a billionaire.

“They might fly on a private jet and have multiple homes,” he said. “And aside from maybe philanthropy,” their lifestyle would basically look the same.”