This is an easy to read, well-cited article. About 4 to 5% of the US adult population are currently involved in a consensual non-monogamous relationship. That doesn't sound like a huge number, however if you were to consider how that percentage is represented in married or committed couples, other experts, such as Barry McCarthy, put the number around 15-20%. So, that is 15-20% of all married or committed couples have a consensual non-monogamous agreement. And the article reminds us what kinds of relationships CNM includes.