In the five years since Bill Gates and Warren Buffett created the Giving Pledge, 193 individuals have made the simple promise to give more than half of their fortune away in life or in death. This week, another 16 people joined the initiative, including Chobani yogurt founder Hamdi Ulukaya and Scottish oil baron Ian Wood.

Signing the pledge has brought glowing press coverage, video testimonials from Bill Gates and invitations to annual conferences in luxurious resorts with fellow billionaires such as Ray Dalio and Pierre Omidyar.

Less publicized is the fact that the crux of the pledge is subjective. Signatories are under no legal obligation to donate any of their money, and sometimes fail to give away anywhere close to half. Charity regulations and estate law can block public disclosures, and Buffett and Gates don’t ask pledge takers to prove a thing.

“It’s really thinking about how iconic figures providing inspiration and support can inspire and serve as a model for society,” said Robert Rosen, the Giving Pledge coordinator as Director of Philanthropic Partnerships for the Bill & Melinda Gates Foundation. “We aren’t looking to add any additional complexity,” said Rosen.

Public disclosures of lifetime and estate giving of the 10 deceased billionaires who signed the pledge show that fulfillment of the pledge varies widely. Only two have given away more than $1 billion, and they donated the money before the initiative was started.

Long-Term Project

The Giving Pledge emphasizes that it’s a moral pledge. This distinction has a very real legal purpose: it eliminates the ability of Giving Pledge signers to sue fellow billionaires who fail to give, according to David Scott Sloan, an attorney and national head of the estate law practice at Holland & Knight.

“When I give money to charity and I pledge to pay it over five years, I actually sign a contract,” Sloan said. “These are all people who sign lots of pledges like that and wanted, I’m sure, to make it very clear it’s a moral direction as opposed to a legal direction.”

Rosen says the Gates and Buffett effort is a long-term project to reset levels of giving.

“The conversation continues to evolve with what’s expected and what becomes the norm of generosity, both in terms of the impact and the impact it has -- that’s our true north star,” Rosen said. “People do it in different ways and at different times because it’s such a personal decision.”