Endowments of private foundations with assets of less than $50 million grew by 10 percent in 2012 as donors dramatically increased their contributions and investment performance improved, a firm that tracks the foundations reported on Wednesday.

Foundation Source, the largest U.S. service provider for small private foundations, said in a report that assets held by a sample group of foundations grew to $2.1 billion in 2012 from $1.9 billion in 2011, owing to a recovery in financial markets that allowed donors to increase their contributions.

The findings were based on transactions of 732 Foundation Source clients between January 1 and December 31, 2012. The study group increased their grants and charitable donations by 9.2

percent in 2012, from the year before. In 2012, they gave $215.7 million in the aggregate, compared with $197.5 million in 2011.

The foundations were able to replenish their coffers by adding $1.06 for every dollar they spent on grants and charitable expenses, up from 93 cents for every dollar spent in 2011.

The report is a snapshot of the activity of 98 percent of the 86,000 private foundations in the United States that have assets of less than $50 million. The 86,000 altogether hold roughly $550 billion.

“The information, on what they are spending, how much new money is coming in, and what their allocations are, is very helpful to me in creating a strategy to help foundations manage their money,” said Phil Shaffer, managing director of wealth management and institutional consulting director at Graystone Consulting, a division of Morgan Stanley.