The study, titled Project Sexus, asked 47,000 people whether they had been unfaithful to their current partner.
19 percent answered that they had been unfaithful.
Married people are more likely to have cheated on their spouse than unmarried people, the survey also found.
For unmarried people in a relationship, 12 percent said they had cheated on their current partner, while the proportion was 15 percent for divorced and separated people.
That figure rose to 22 percent for people who are currently married.
More men have cheated on their partner than women, according to the survey. Almost 1 in 4 men said they had been unfaithful to their current partner, while 14 percent of women responded in the affirmative to the same question.
The study asked respondents only about their current relationships and not whether they had been unfaithful to past partners.