Abstract Study question How much do the general population know regarding the menstrual cycle and conception? Summary answer There is a lack of basic knowledge regarding key menstrual cycle and conception facts which could lead to missed reproductive opportunities. What is known already Although the human menstrual cycle is a “normal” biological process, stigma remains regarding open discussion of periods, and there is limited research surrounding the public understanding of the menstrual cycle and conception. Infertility rates are rising globally. With people commencing a family later in life, it is essential that the knowledge needed to make informed decisions regarding conception is prevalent. The primary aim of this study was to determine the general populations’ knowledge regarding the menstrual cycle and conception. Study design, size, duration A prospective, voluntary, anonymous, self-completed ethically approved questionnaire was distributed internationally online via various social media platforms over a period of 3 months. Participants/materials, setting, methods In total, 676 fully completed questionnaires were analysed. 84.9% of participants identified as female, 13.5% identified as male, and a small remainder of the participants identified as non-binary (1.6%). Most participants were white (87%), lived in the UK (92%) and had a university education (62.1%). 12% of the respondents were healthcare workers of any type and 31.7% had biological children. Main results and the role of chance Female participants selected correct answers at higher rates than both males and non-binary participants for 88.9% of the questions. No differences in correct answers were seen when people with and without children were compared and those with university education versus those without. Some questions received a high number of correct answers by all participants; ‘What is menopause?’ (98.8% correct), ‘What does PMS stand for?’ (86% correct), ‘How many days does the average menstrual cycle last?” (89.2% correct), ‘Is it possible to get pregnant on your period?’ (77.4% correct). Whereas other questions were answered poorly by most participants; ‘How many days per month, on average is it possible to get pregnant?’ (40.9% correct), ‘What counts as the first day of a new menstrual cycle?’ (54.71% correct), and ‘How many days does the average period last?’ (56% correct). Limitations, reasons for caution The majority of participants were white, lived in the UK and the questionnaire was accessed through an online medium. Responses from non-white participants, outside of the UK and from those without access to the internet may have captured further themes in relation to the menstrual cycle and conception knowledge. Wider implications of the findings Increased education is urgently needed to ensure knowledge is sufficient for people to access healthcare when required and understand the principles of conception and fertility to fulfill or prevent when coveted. This data will facilitate the understanding that there is a need for sexual and reproductive education among the public. Trial registration number NA