It's about $75,000 in income a year.
In this Princeton study reported by the LA Times, researchers found that after reaching an income of $75,000 per year, money can't buy happiness. However, earning more than that can help people view their lives as being being more successful or better.
The study found that people's evaluations of their lives improved steadily with annual income. But the quality of their everyday experiences -- their feelings -- did not improve above an income of $75,000 a year. As income decreased from $75,000, people reported decreasing happiness and increasing sadness, as well as stress. The study found that being divorced, being sick and other painful experiences have worse effects on a poor person than on a wealthier one.
"More money does not necessarily buy more happiness, but less money is associated with emotional pain," the authors wrote. "Perhaps $75,000 is a threshold beyond which further increases in income no longer improve individuals' ability to do what matters most to their emotional well-being, such as spending time with people they like, avoiding pain and disease, and enjoying leisure."