Wealth is much more concentrated than income, and wealth might be more important. The top 1% of Americans own 43% of total wealth, and the top 0.1% own 22%.
Also, the higher your income, the larger the fraction you can comfortably donate. Something much higher than 10% of total potential donated income will be in the top 1%.
This underestimates the potential donations from people who don't have high net worth. Wealth is largely a function of what percentage of income you put into savings, which is much higher for wealthier people. But you can donate out of your income, not just out of your savings. At the same time, if you're not saving much money then you might not have much wiggle room in your budget to donate more, so this maybe isn't a huge consideration.
Wealth is much more concentrated than income, and wealth might be more important. The top 1% of Americans own 43% of total wealth, and the top 0.1% own 22%.
Also, the higher your income, the larger the fraction you can comfortably donate. Something much higher than 10% of total potential donated income will be in the top 1%.