'Tis the season to give to charity, so you might as well make an "impact," said Tim Freundlich, president of ImpactAssets.

Freundlich said there are four ways investors can double the impact of their philanthropy. First, they can give appreciated securities. Second, they can align impact investing with philanthropic giving. Third, they can make philanthropy a family affair. And four, they can use a Donor-Advised Fund to make impact investments.

Freundlich said impact investing is a growing trend, with about 30% of charitable donors already engaged in impact investing. And he added that donors supporting social enterprises -- like microfinance -- don't have to sacrifice returns to make an impact.