He's probably taking the tax deductions for the donations, so it's not the same as donating an additional 50% "from the remaining money" (as some of it comes ou

He's probably taking the tax deductions for the donations, so it's not the same as donating an additional 50% "from the remaining money" (as some of it comes out of what would have been taxes). I didn't see it explicitly one way or the other in the article, though, so he could be donating 50% while still paying taxes on the full 100%.