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On the surface, tech billionaires are very, very generous people.

But when you dig into the numbers, a more complicated portrait emerges.

New data collected by the Chronicle of Philanthropy offers the best yearly snapshot of the United States’ 50 biggest philanthropists, and it’s no surprise that technologists once again rank among the biggest givers. That’s because they’re also the country’s richest people.

And you need to put those two facts — the scale of their generosity and the scale of their bank accounts — side by side when assessing their commitments to charity. That’s an essential assessment given that billionaires often use their philanthropy to resist attempts by governments to tax more of their wealth, even as some leading Democratic presidential candidates like Sens. Bernie Sanders and Elizabeth Warren say they will tax the wealthy more if they’re elected in November.

Let’s not overgeneralize: Eric Schmidt, the largest tech philanthropist of 2019, gave $1.3 billion to charitable efforts. And while I have some concerns about the impact of the things Schmidt is funding, he committed about 9 percent of his net worth to the cause. That’s a lot.

Sheryl Sandberg has a net worth of $1.7 billion, meaning she devoted about 7.5 percent of her money to charitable causes with her $128 million in gifts.

But others on the tech philanthropy leaderboard? The headline figures are big, but they shrivel when put against their net worths.

Mark Zuckerberg gave just about as much as Sandberg to charity, but his $110 million is just 0.2 percent of his total assets, though a spokesperson for Zuckerberg’s personal philanthropy noted that it distributed $420 million in grants to nonprofits in 2019.

That’s 0.2 percent is the same percentage gifted by Sergey Brin, who ranked as the sixth-most generous tech philanthropist in 2019 (and he is putting money behind some innovative efforts).

Pierre Omidyar and Marc Benioff, who consistently rank among the industry’s most generous givers, sat in third and fourth place on the most recent list; both sent out about 3.5 percent of their net worths in 2019. (An Omidyar foundation has provided a grant to fund Recode’s Open Sourced project.)

And keep in mind, these are the country’s most generous donors. There are some major tech philanthropists who would make these donation rates seem like less of a pittance.

To be sure, donating hundreds of millions to charity — regardless of whether it’s motivated by tax reasons, spent on misguided projects, or buys them unmerited PR value — isn’t something that most people can boast of. So it’s easy for outsiders to attack them. But the percentage is important. Philanthropy journalist Marc Gunther points out that, dating back to the biblical notion of tithing, charitable gifts historically were weighed against the person’s resources.

And here’s the ultimate catch: Even as rich people strive to give away their money — some as part of intentional, well-meaning projects like the Giving Pledge — they keep getting richer.

For instance, consider Schmidt. Yes, he gave away $1.3 billion in 2019, cementing him as the country’s second-biggest philanthropist, regardless of industry. But his net worth grew by $3 billion during that same time period.

Brin and Zuckerberg both gave away $110 million in 2019. But Brin’s net worth grew by $14 billion, and Zuckerberg’s grew by $26 billion.

Needless to say, Zuckerberg’s charitable gifts are not making a dent in his attempt to part with all of his money before he dies. The same is true for most of the country’s biggest donors.