they are required to donate 5% of their equity each year to retain their tax exempt status with IRS. most charities do it this way including the biggest one - bill and melinda gates foundation.
it's important to say that Bill Gates doesn't give charity his own taxed income... by moving his equity into his foundation, he is essentially avoiding capital gains tax and dividend tax. I'm not saying that taxes are good but we all have to pay them. super-rich have all these smart schemes to pay in taxes as little as possible.
As long as Bill Gates foundation spends 5% of his equity on charity annually, you can't call him philanthropist since 5% rate is exactly what IRS requires charities to do as long as they want to keep their tax exempt status. When Bill Gates starts giving to charity more than he is legally required, then I'll change my opinion.
