Contributions to charities through Schwab Charitable, a donor-advised fund, increased by 15 percent last year, Schwab announced Tuesday.

Schwab Charitable distributed more than $1 billion to 58,000 charities on behalf of donors in 2015. Feeding America, Doctors without Borders, Red Cross and The Salvation Army were among the not-for-profits that received the most grants.

“We are so thankful that our donors continued to give generously in 2015 even as stock markets became more volatile,” says Kim Laughton, president of Schwab Charitable.

Schwab Charitable is working with donors and charities to increase the percent of disposable income Americans donate to charity. The figure has hovered around 2 percent of disposable income for the past 40 years, Schwab says.

Almost two-thirds (63 percent) of contributions to Schwab Charitable accounts in 2015 were appreciated assets, including publicly traded stock and more complex assets such as restricted stock, privately held shares, initial public offerings, real estate, private equity and hedge fund interests.