Most Americans who give to nonprofits overestimate their generosity, according to a recent report from Grey Matter Research and Consulting.

Just 8 percent of American donors give 10 percent or more of their household income to charitable organizations and places of worship, the report found. Yet the average donor believes he or she gives 8.4 percent of household income to charitable organizations, not including places of worship — a figure that far exceeds reality.

Nearly 9 in 10 donors overestimate the proportion of their household income given to nonprofit organizations. The estimates aren’t just slightly exaggerated; they’re usually far off base. In fact, the average donor overestimates the proportion of income he or she gives to charity by 331 percent. And 6 out of 10 donors believe they give at or above the proportion of their income that the average American donor gives.

“All this adds up to a picture of donors who truly believe they’re doing far more than they’re actually doing, and far more than most other people are doing,” the report concludes.

Grey Matter is a research group serving nonprofit organizations.