Philanthropic donations made through the charitable-savings arm of Fidelity Investments reached a record $3.1 billion last year, the most given away since the program began in 1991.

The money came from donor-advised funds — Fidelity Charitable calls them “giving accounts’’ — that are managed by Fidelity and allow people in all income brackets to become miniature philanthropists. When donors contribute to their funds, they receive an immediate tax deduction but face no deadlines on how quickly — if ever — they must give the money away.

Donor-advised funds have become increasingly popular and are now offered by numerous banks and investment firms, as well as by groups such as the Boston Foundation and Combined Jewish Philanthropies.

The funds have also become the subject of criticism from detractors who say they contain too much money sitting idle rather than being put to quick charitable use. To remedy that, some critics advocate mandatory payout rules.

In 2015, Fidelity Charitable said Thursday, its donors made 733,000 grants ranging in size from $50 (the minimum payout permitted) to several million. The average grant was $4,200, and the money was distributed among about 106,000 charities nationwide.

“Despite the market downturn this year, our donors continued to show dedication to giving back,’’ said Fidelity Charitable president Amy Danforth. “Donors who contribute to donor-advised funds irrevocably commit those funds to philanthropy. This makes their ability to give — year in and year out — less sensitive to market fluctuation and provides a source of ongoing support to thousands of charities nationwide.’’

Since its inception, Fidelity Charitable, which manages more than 80,000 donor-advised funds, has made more than $21 billion in grants. Last year’s giving rose 18 percent over the previous year.

In addition to cash, Fidelity Charitable donors can contribute stocks, mutual funds, real estate and, as of November, Bitcoin to their accounts. Once donors decide which charities will benefit, Fidelity sends their donations to the selected eligible nonprofits. Contributions to the funds can only be used for charitable purposes and cannot be rescinded.

Fidelity describes donor-advised funds as a way to “democratize’’ charitable giving by making it simpler and more accessible. Fidelity Charitable donors, for example, can manage their accounts entirely online.

Sacha Pfeiffer can be reached at pfeiffer@globe.com. Follow her on Twitter at @SachaPfeiffer.