Do Periods Sync Up?

Nothing says solidarity with the sisterhood like finding out you have the same menstrual cycle as your best friend or loved one! In fact, the first thing you probably thought was “we’ve been spending too much time together”, right? We’ve all been there!

But does spending time with other people with periods actually sync your menstrual cycles? Or is it more period mythology, like not being able to go swimming in the sea on your period because of sharks?

Read on to find out whether your period is actually syncing up with your household.

Do periods sync up?

Yes! And no…

An entire study published in 1971 by Martha McClintock analysed the cycles of 135 people with periods living in the same dorm, with the results suggesting that periods do occur at similar times when people eat meals together, stress together, or just spend time together.


Since 1971, there have been other studies carried out that don’t support Martha’s McClintock’s findings:-

  • In 1993, a study investigating the same thing in cohabiting lesbian couples found no evidence of menstrual cycles synchronising
  • In 1991, a study including 132 sorority members and roommates found the same – in fact, the cycles moved further apart
  • In 1994 Israeli basketball players were examined and similarly came to the same conclusion
  • And a 2006 study on 186 Chinese people with periods living in a college dorm found that their periods didn’t sync up. At all.

Most recently, Clue App – the menstrual cycle tracker – reached out to their users for a study. They narrowed down the data set to 360 pairs; siblings, roommates, partners… and reviewed their cycles over a three-month period. Their study actually found that periods were more likely to become OUT of sync over time.

Check out Clue’s findings here.

TLDR; the results of the studies are contradictory and we still don’t have a final answer!

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So, why do we believe our menstrual cycles match up?

According to Beverly Strassman’s paper, with a 28-day cycle, a maximum of 14 days apart, and a period lasting around 5 days, there’s no doubt that our menses will and can crossover. Plus, we’d absolutely want to believe this is the case when our headaches are rife, the spots are shining on our faces, and we need someone in the same boat as us to vent to.

The human brain loves finding patterns, so we’re more likely to take note when we have our period at the same time as a loved one than not. Over time, this also creates an illusion of becoming synchronised!

While there’s no definitive answer across all the studies, we can at least find comfort in knowing someone else is experiencing what we are in the same week too. 😅

Do you think our cycles can synchronise? Let us know in the comments below!

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