NEW YORK — United Way, ranked as America’s largest charity for all but one of the past 25 years, has been emphatically knocked from that spot by Fidelity Charitable, the leader of a rapidly growing philanthropic sector that is transforming the way many Americans give.

Boston-based Fidelity, which collected $4.6 billion in private donations in 2015, is a donor-advised fund — an increasingly popular type of charity to which a donor can make a contribution, immediately receive a tax benefit, and then recommend grants from the fund at any time thereafter.

The new rankings released Thursday by the Chronicle of Philanthropy showed that Fidelity’s private support rose nearly 20 percent from 2014, when it narrowly trailed United Way. The new data showed United Way in second place, with $3.7 billion in support — down 4.2 percent from 2014.

Feeding America, which supplies many food banks in the U.S., was third in the new rankings, followed by a California-based donor-advised fund, the Schwab Charitable Fund. Catholic Charities USA ranked fifth, the Salvation Army was sixth.

Since 1991, when the Chronicle of Philanthropy started its rankings, United Way had been the largest charity in every year except 2006, when the Salvation Army took the top spot.

Brian Gallagher, president of United Way Worldwide, attributed the shift to economic trends, including a surge in giving by the weathy and stagnating wages for many of the middle-class Americans who have been loyal United Way donors. United Way’s average contribution is $365, while the minimum a donor must give to contribute to Fidelity Charitable is $5,000, and the average account size is about $15,000.

“We see it as a good thing — we don’t see it as competitive,” said Gallagher, noting that United Way receives some donations via donor-advised funds.

Founded in 1991, Fidelity is nearing its goal of allocating $25 billion in charitable grants over its first 25 years. Last year, its 132,000 donors recommended $3.1 billion in grants to support more than 106,000 organizations across the U.S. and abroad — making it the nation’s second-largest grant-maker behind the Bill & Melinda Gates Foundation.

Pamela Norley, who became Fidelity’s president in August, said its donors appreciate technological arrangements that facilitate online giving and tax-related record-keeping.