NEW HAVEN, Conn. (AP) – Yale University’s endowment earned a 22.9 percent return in the past fiscal year, to bring the total endowment to $18 billion, the university’s investments office announced Monday.

The university is spending about $676 million from the endowment this year, or about 34 percent of the university’s revenues. School officials said the endowment is Yale’s single largest source of budgetary support.

Yale has the second-largest endowment of any private university in the U.S.

The share of the operating budget provided by the endowment has more than doubled in the past decade.

A study by the National Association of College and University Business Officers ranked Harvard University’s endowment as the largest, at about $29.2 billion.