The hidden wealth is roughly equal to the annual GDP of the U.S. and Japan combined. The report was commissioned by the Tax Justice Network based in the UK. The report claims to be the most extensive ever on the "offshore economy".
The report was researched and written by James Henry an expert on tax havens.
The tax income lost is sufficient to make a significant difference in the finances of many countries. In fact Henry claims that if these offshore funds were repatriated some debtor countries would turn out to be wealthy!
Henry notes that the hidden assets are not held by some obscure financial institutions in small island nations. The companies holding these assets are among the biggest names in finance: UBS, Credit Suisse, and Goldman Sachs. These three handle the most assets offshore.
The super-rich elite comprise 92,000 people or .001 per cent of the world's population are claimed to have 21 trillion in hidden assets. Henry collected data from the IMF, the World Bank, and the bank of International Settlements. Even these figures do not take into account other wealth embedded in property such as yachts and other assets.
The full report can be seen here.
Another tax expert John Whiting a UK government adviser doubted that the amount hidden was so large. Whiting who is director of the Office of Tax Simplification said:: "There clearly are some significant amounts hidden away, but if it really is that size what is being done with it all?"" For more on the report see this article and also here