You were taxed when you received that money, so you don't have $1000, you only have $700 (assuming a 40% tax rate - sub in your own rate as applicable). If you

You were taxed when you received that money, so you don't have $1000, you only have $700 (assuming a 40% tax rate - sub in your own rate as applicable). If you get a tax deduction for giving to Watsi, you can give them $1000 and only lose $700 out of pocket. If you do not get a tax deduction for giving to Watsi, then you can give them $700 and lose $700 out of pocket. In either case, you are giving them $700 out of pocket.