There are more than two million nonprofits operating in the United States — roughly one for every 135 Americans. As the season of giving ramps up, how can you feel confident that your dollars will be spent responsibly? “If you find yourself considering a gift to charity that called you on the phone, you’ve already lost most of the battle to do as much good as possible,” writes Elie Hassenfeld, co-founder and co-executive director of GiveWell, an organization that highlights a few of the most effective nonprofits. “If you wait for charities to come to you, you’re just rewarding the ones that are most aggressive — not the ones that do the most good.” Read on to learn how you can avoid donor’s remorse.