How to tax billionaires—and how not to

Cash-strapped governments want to get their hands on a slice of these riches. Next year Australia will start taxing unrealised gains in employee pension-fund accounts with balances of more than A$3m ($2m). As part of his re-election campaign, President Joe Biden is promising to find $500bn over ten years for social programmes by charging a 25% tax on the unrealised capital gains of individuals who, like Mr Huang and 10,000 other Americans, are worth $100m or more.