This study examines an inconsistency between an attitude and a behaviour: non-use of contraception among people who are not trying to get pregnant. More than one in four people in that situation report not using contraception ‘sometimes’ or ‘always’ and consequently face the risk of pregnancy. We test three potential explanations: acceptability of having (further) children; perceived low pregnancy risk; and perceived social pressure. Using 10 waves of the German pairfam panel, we estimate sex-specific between–within models, where each explanation is tested by several indicators. We find evidence for the explanation of a(nother) child being considered acceptable: a positive fertility desire increases contraceptive non-use among women and men, and relationship duration increases it among women. Supporting the explanation of low perceived pregnancy risk, analyses show that perceived infertility, breastfeeding, and age increase the probability of non-use of contraception for women and men. However, there is no strong evidence for perceived social pressure affecting contraceptive non-use.