Reported in Feb, 1989, Confident Living, p. 20.
The study found that households with incomes below $10,000 give away an average of 2.8% of their income, while households with incomes between $50,000 and $100,000 give away only 1.5%. Nearly half of the total contributions to charity in the U.S. comes from households with incomes below $30,000. The average total giving to charity per household was $790.
(From Independent Sector, a Washington based non-profit organization that recently conducted a study on giving to charity)