We don’t sync up with each other. Research conducted by the menstrual app Clue found that rather than menstrual synchronicity occurring among menstruators who live together, their periods were more likely to diverge over time. If there are periods of time when you menstruate at the same time as someone you live with, it’s likely because cycles vary in length for some individuals as well as varying between different individuals, so it makes sense that there will be periods of overlap when you’re bleeding together.