“Smart donors have been playing timing games with the charitable deduction for a long time,” said Roger Colinvaux, a tax professor at the Catholic University of America’s Columbus School of Law. “In this case, he potentially gets a very large deduction and gives nothing away. That’s a disturbing public policy issue.”

On Reddit, Mr. Woodman suggested that his wealth was reaching charities: “The Foundation has gone on to fund causes supporting women and children and will continue to do so!!!!” Just how much money has gone to which organizations, of course, remains a mystery.

Wall Street Fees

When it comes to D.A.F.s, the United States tax code rewards the promise of good intentions. Wealthy donors — including many of the Silicon Valley billionaires who have asked the public to trust them with their digital lives — pledge to distribute their funds to charity once they get their tax break. But in the absence of rules requiring donors to give their money away, it is hard to know what public good comes in exchange for those lucrative write-offs.

Skeptics see a system ripe for abuse. Donors might wait years to engage in meaningful philanthropic activity, or decide to simply leave the fund for their children to manage.

“We’ve put this rule in place that says you get maximum tax benefits when you make a donation,” said Ray Madoff, a professor at the Boston College Law School and a vocal critic of donor-advised funds. “But you don’t have to do anything with it.”

Ms. Norley of Fidelity Charitable argues that on balance, account holders are generous. At her organization, roughly a quarter of the assets held in D.A.F.s have been distributed to nonprofits in each of the past two years. Other sponsor organizations report similar distribution rates.

Yet such statistics can be skewed. In many instances, these figures include transfers from one D.A.F. to another. In the most recent fiscal year, for instance, Vanguard Charitable sent more than $15 million from its D.A.F.s to Fidelity Charitable. Sponsor organizations say this is simply a matter of wealthy donors adjusting their accounts. But it also creates the illusion of meaningful philanthropic activity where there is none.