It's boom time for billionaires: 2019 saw the net worth of the world's richest 500 people soar by 25 per cent.

The Bloomberg Billionaires Index says the collective net worth of the world's 500 wealthiest individuals totals $5.9 trillion, up $1.2 trillion in just 12 months.

American billionaires alone added $500bn to their wealth, with Facebook founder Mark Zuckerberg adding $27.3bn and Microsoft co-founder Bill Gates adding $22.7bn.

Just 52 people on the list saw their wealth decline in 2019, according to Bloomberg. Among them was Amazon's Jeff Bezos' worth fell by $9bn, mainly due to his divorce settlement.

Don't feel too sorry for him, though, as he remains the world's richest person.

The report drops amid a Democratic primary campaign in which wealth disparity is a hot topic.

A report earlier this year found that income inequality in the United States is at its highest point since data started being collected more than 50 years ago.

Progressive politicians have recently called for tougher tax policies for the ultra-rich; Alexandria Ocasio-Cortez called for people to "tax the rich" as Democrats argued over Elizabeth Warren's tax proposal at a primary debate in October.

Warren has made a wealth tax a centrepiece of her campaign. The proposal calls for imposing a 2 per cent tax on the wealth of people with more than $50m in assets, while those with assets more than $1bn would face a 3 per cent tax.

Forbes' top 25 most powerful women in the world for 2019 Show all 25 1 /25 Forbes' top 25 most powerful women in the world for 2019 Forbes' top 25 most powerful women in the world for 2019 1. Angela Merkel German chancellor Getty Images Forbes' top 25 most powerful women in the world for 2019 2. Christine Lagarde President of the European Central Bank Getty Images Forbes' top 25 most powerful women in the world for 2019 3. Nancy Pelosi Minority leader of the US House of Representatives AFP via Getty Images Forbes' top 25 most powerful women in the world for 2019 4. Ursula von der Leyen President of the European Commission POOL/AFP via Getty Images Forbes' top 25 most powerful women in the world for 2019 5. Mary Barra CEO of General Motors Getty Images Forbes' top 25 most powerful women in the world for 2019 6. Melinda Gates Co-chair of the Bill and Melinda Gates Foundation Getty Images Forbes' top 25 most powerful women in the world for 2019 7. Abigail Johnson CEO of Fidelity Investments Getty Images Forbes' top 25 most powerful women in the world for 2019 8. Ana Patricia Botín Chair of Santander Group Getty Images Forbes' top 25 most powerful women in the world for 2019 9. Ginni Rometty CEO of IBM Getty Images Forbes' top 25 most powerful women in the world for 2019 10. Marillyn Hewson CEO of Lockheed Martin Forbes' top 25 most powerful women in the world for 2019 11. Gail Boudreaux President and CEO of Anthem Getty Images for Women's Sports Forbes' top 25 most powerful women in the world for 2019 12. Susan Wojcicki CEO of YouTube Getty Images Forbes' top 25 most powerful women in the world for 2019 13. Isabelle Kocher CEO of Engie AFP via Getty Images Forbes' top 25 most powerful women in the world for 2019 14. Safra Catz Co-CEO of Oracle AFP via Getty Images Forbes' top 25 most powerful women in the world for 2019 15. Kristalina Georgieva Managing director of International Monetary Fund AFP via Getty Images Forbes' top 25 most powerful women in the world for 2019 16. Julie Sweet CEO of Accenture Forbes' top 25 most powerful women in the world for 2019 17. Emma Walmsley CEO of GlaxoSmithKline AFP via Getty Images Forbes' top 25 most powerful women in the world for 2019 18. Sheryl Sandberg COO of Facebook Getty Images Forbes' top 25 most powerful women in the world for 2019 19. Ruth Porat CFO of Alphabet Getty Images for Fortune Forbes' top 25 most powerful women in the world for 2019 20. Oprah Winfrey Entrepreneur, television personality and philanthropist NBCUniversal via Getty Images Forbes' top 25 most powerful women in the world for 2019 21. Judith McKenna CEO of Walmart's international division Getty Images for Fortune Forbes' top 25 most powerful women in the world for 2019 22. Jessica Tan Co-CEO of Ping An Group YouTube/Massachusetts Institute of Technology (MIT) Forbes' top 25 most powerful women in the world for 2019 23. Ho Ching CEO of Temasek Getty Images Forbes' top 25 most powerful women in the world for 2019 24. Phebe Novakovic CEO of General Dynamics AFP via Getty Images Forbes' top 25 most powerful women in the world for 2019 25. Shari Redstone Chairwoman of ViacomCBS

The increase in billionaires' wealth also comes in the first full year since the passage of the Republican tax law.

A report by the Congressional Research Service in May of this year said the tax law's effect was smaller on the economy than many forecasters had predicted and growth was not consistent "with the direction and size of the supply-side incentive effects one would expect from the tax changes."