Starting and stopping oral HIV pre-exposure prophylaxis (PrEP) in a way that compromises its effectiveness should be avoided. Between September 2020 and June 2021, we assessed self-perceived and actual knowledge of effectively starting and stopping oral PrEP through an online survey among 206 PrEP users assigned male at birth in Belgium. We examined associations between incorrect start-and-stop knowledge and socio-demographics, sexual behaviour and PrEP use, using bi- and multi-variable logistic regression. The majority of men (84.9%) perceived their start-and-stop knowledge as 'very good', but only 62.1% of all men correctly indicated how to effectively start and stop with PrEP. Using PrEP daily [adjusted OR 2.12, 95% CI (1.06-4.28), p = 0.034] was significantly associated with incorrect start-and-stop knowledge. To enable PrEP users to effectively use PrEP, they need to be better informed about how to start and stop use, irrespective of the dosing regimen.