Americans are now donating to charities and nonprofits at a record-high rate of more than $1 billion a day, according to the latest comprehensive report on the nation's charitable giving.

The Giving USA report, being released Tuesday, said giving from individuals, estates, foundations and corporations reached an estimated $373.25 billion in 2015, setting a record for the second year in a row. The total was up 4 percent from $359 billion in 2014.

By some barometers in the report, however, Americans are not getting more generous. For 2015, giving by individuals represented 2 percent of total disposable income — down from 2.4 percent in 2000 and the same as the rate in 1975.

Similarly, total charitable donations have hovered around 2 percent of the gross domestic product for many years. For 2015, that figure was 2.1 percent, the same as in 2014 and slightly above the 40-year average of 1.9 percent.

Out of the nine charitable sectors, the biggest increase in 2015, percentage-wise, was for organizations involved in international affairs. Giving to this sector rose 17.4 percent, when adjusted for inflation, to $15.75 billion. Giving to education rose nearly 9 percent to $57.48 billion; this includes many multimillion-dollar gifts to colleges and universities.

As usual, the largest share of donations — $119.3 billion — went to religious organizations. But the increase for this sector was modest at 2.6 percent.

Foundations were the only sector to experience a decline in charitable gifts, which dropped 4 percent to $42.26 billion.

Giving by individuals accounted for $264.58 billion of the total, while corporate giving added up to $18.45 billion. The rest came from foundations and charitable bequests.

The report noted that the increased giving for 2015 followed an even bigger increase in 2014 — up by 6.1 percent when adjusted for inflation.

"It's heartening that people really do want to make a difference, and they're supporting the causes that matter to them," said W. Keith Curtis, who chairs the Giving USA Foundation.

The report attributed the two-year surge to a continued economic recovery, including a more stable financial situation for many households.

The annual Giving USA report is published by the Giving USA Foundation. It is researched and written by staff at Indiana University's Lilly Family School of Philanthropy.