That would be more accurate, but doing it well would start to feel like a tax return. But going on income alone without considering cost of living, debt obligations, family size, etc. would produce inaccurate results.
Maybe it could be a range—e.g., We recommend the average person earning $80K a year donate 11%; for most people at this income we would recommend donating somewhere between 8-14% depending on personal circumstances. (I changed 10 percent from your example to 11 percent as a starting point, because I think the median person would assign themselves a slightly-less-than-median point in the range.)
That would be more accurate, but doing it well would start to feel like a tax return. But going on income alone without considering cost of living, debt obligations, family size, etc. would produce inaccurate results.
Maybe it could be a range—e.g., We recommend the average person earning $80K a year donate 11%; for most people at this income we would recommend donating somewhere between 8-14% depending on personal circumstances. (I changed 10 percent from your example to 11 percent as a starting point, because I think the median person would assign themselves a slightly-less-than-median point in the range.)