Though many Americans attend churches that preach tithing, few U.S. adults practice it, and the percentage of givers is shrinking with each generation, according to a recent Barna Group report, “The Generosity Gap.”

Just 1 percent of Millennials (those born between 1984 and 2002) give 10 percent or more of their income to a church. By comparison, 2 percent of Gen-Xers (born between 1965 and 1983); 3 percent of Baby Boomers (born 1946 to 1964); and seven percent of Elders (born before 1946) tithe.

Three percent of Millennials, 4 percent of Gen-Xers, 5 percent of Boomers and 8 percent of Elders give at least 10 percent of their income to a nonprofit.

Barna attributes generational giving differences in part to the decline in faith and church attendance among younger Americans. Millennials increasingly identify as atheist, agnostic or religiously unaffiliated — religious “nones.”

“As the proportion of Christians in the U.S. continues to shrink with each successive generation, the base of givers and volunteers on whom churches and Christian nonprofits depend is also shrinking,” the report says. “Practicing Christians — who say their faith is very important in their life and have attended a worship service within the past month — are a diminishing slice of the overall population.”

In addition, Barna notes that many younger Americans continue to struggle financially in a post-recession era. Today’s workers are also more likely to engage in freelance work, resulting in less predictable incomes and fewer steady paychecks compared to previous generations.