Conservative estimates are that 60 percent of men and 40 percent of women will have an extramarital affair. These figures are even more significant when we consider the total number of marriages involved—since it's unlikely that all the men and women having affairs happen to be married to each other. If even half of the women having affairs (or 20 percent) are married to men not included in the 60 percent having affairs, then at least one partner will have an affair in approximately 80 percent of all marriages.
But we need to take a closer look at the statistics on affairs to determine what they can contribute to an understanding of our sexual patterns. While affairs happen in non-marital, "committed" relationships as well as within marriage, most of the statistics deal only with "extramarital" affairs. These statistics began with Kinsey's reports in the 1940's and early 1950's. Kinsey's samples included 5,000 men and showed that by age 40, 50 percent of the men had experienced extramarital sexual intercourse. Kinsey's original samples of 6,000 women showed that by age 40, 26 percent of the women had experienced extramarital sexual intercourse.
Later studies dealing exclusively with men indicate a continuous increase in the number of men having extramarital affairs. The increase for women having affairs has been even more significant. Some of the statistics, both for men and for women, are extremely high and legitimately debated, but many people question any statistics on extramarital affairs, arguing that statistics are unreliable and confusing and that no one knows precisely how prevalent affairs are. While there are slight differences in the estimates based on clinical studies and questionnaires, the bottom line is compelling in showing an extremely high (and rising) incidence of extramarital affairs.