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Published Research

How does Natural Cycles Work with Irregular Cycles?

Illustration of circles and semi circles in different colours

Key takeaways

  • Natural Cycles birth control is as effective with irregular cycles as with regular cycles
  • Users with irregular cycles may experience more red days to ensure the app’s effectiveness

In this analysis, we investigated if users with irregular cycles (shorter than 21 days or longer than 35 days) can use Natural Cycles with the same effectiveness rate as those with regular cycles. 

We looked at the data from over 20,000 users, who were divided into two groups based on if they reported their cycle to be regular or irregular. Around 20 % of Natural Cycles users have irregular cycles, meaning their cycles are shorter than 21 days or longer than 35 days, or their cycle length changes by more than 10 days.

The two groups were then compared to see if the effectiveness of the app was the same.

The most important finding was that neither changing cycle length nor having very long or short cycles affected the effectiveness of Natural Cycles, meaning that it is just as effective as birth control regardless of whether or not your cycle is regular. To maintain the app’s effectiveness, users with irregular cycles will get more red (fertile) days to account for their fertile window varying.