Little is known about how common sexual agreements (SAs) are among mixed-sex couples. Data from 555 partnered, mixed-sex adults who completed a 1-time web survey were used to describe who had a SA in their current relationship and associated factors. Sixty-two percent reported having a SA. Having a SA was associated with identifying as bisexual or questioning, owning a smartphone, and recently having anal sex in the current relationship. Further research is needed to assess whether SAs may be an ideal platform to assist mixed-sex couples with their sexual health needs, which could include HIV/STD prevention and family planning.