The new lover is most often a friend or co-worker, and the typical fling lasts less than a week.
Survey takers guessed that twice as many people are having extramarital affairs as really are, estimating that 44 percent of married men and 36 percent of married women are unfaithful.
The reality is it's not as rampant as we think, with 28 percent of married men and 18 percent of married women admitting to having a sexual liaison, the survey found.
Few cheaters — only 2 percent — were busted in the act.
And even when confronted with a partner's suspicions, only 6 percent of both men and women confessed to having an affair.
For most people in relationships, a commitment means no playing around, ever.
That doesn't mean there aren't plenty of love rats out there.
About three-quarters of the survey takers say they've made a monogamous commitment, with a majority either married or remarried.
But a significant portion found it easier to make that promise than keep it.
"We think everybody is out there doing it," says Janet Lever, a sociologist at California State University, Los Angeles, and the study's lead researcher.
"Well, they're not." In fact, the rate of cheating has stayed pretty consistent, according to research expert Tom W.
"It is surprising that the wives and husbands and girlfriends aren't more suspicious," says Lever.