George Soros is giving his foundation a big inflow of money in part to minimise a tax bill hedge fund managers are facing this year.

Money managers have until the end of the year to pay taxes on fees they earned from investors in offshore funds and had deferred payment on. Many are now turning to charitable donations -- including to their own foundations -- to help offset the levies coming due.

George Soros is giving his foundation a big inflow of money in part to minimise a tax bill hedge fund managers are facing this year. Credit:AP

Soros, founder of $US26 billion Soros Fund Management, has transferred almost $US18 billion to his Open Society Foundations over the past several years, according to a foundation official.

Only the Bill & Melinda Gates Foundation is now larger than Open Society among US grant-making groups, with an endowment of about $US40 billion. Soros is worth an estimated $US23 billion, according to Forbes.