As many as 50 million people now have a record of their menstrual cycle on their personal devices. But evidence about the apps’ accuracy and quality suggest they don’t always help us better understand our bodies.
Dr Tessa Copp from the School of Public Health in the Faculty of Medicine and Health and Dr Emmalee Ford from the University of Newcastle explained what period-tracking apps can – and can’t – tell you about your cycle in an op-ed for The Conversation.
Period trackers ask users to enter a large amount of personal data, including period dates, sexual activity, mood, symptoms (such as bloating or cramps), and energy levels. Based on this self-reported data, the apps use algorithms to make predictions.
These include when your period will arrive, how long it will last, the day you’ll ovulate and your “fertile window”, usually about 3–7 days per cycle when conception is more likely.
Many apps aren’t transparent about how they formulate predictions, and whether they are applicable to most users, warn Dr Copp and Dr Ford, noting some apps don’t include biometric data in their algorithms even if they record it.
Many calendar-based apps predict ovulation as 14 days before the estimated period start date, assuming a textbook menstrual cycle of 28 days. But research since the 1960s has shown the length of menstrual cycles can vary between individuals and from cycle to cycle.
“Studies have shown only 13–16% of women have a 28-day cycle, and only 13% ovulate on day 14,” said Dr Copp and Dr Ford, meaning calendar-based app predictions may be inaccurate for most people.
For those using apps for fertility planning, Dr Copp and Dr Ford note data on effectiveness is limited, and research often excludes participants whose cycles vary.
Apps often market themselves as empowering users, enhancing self-knowledge and control. Many claim to fill the gap in women’s health research.
“But one recent study found people who use period-tracking apps are no more likely to have basic knowledge of their cycles than those who don’t use them,” said Dr Copp and Dr Ford. “Another study found apps improve knowledge, but only slightly.”
There are some benefits to using period-tracking apps, say Dr Copp and Dr Ford. They can give you an instant record of your menstrual cycles and can also be useful as an idea of when your period may arrive.
“But be aware they could be wrong. And given the mounting evidence showing just how much menstrual cycle length can vary, don’t trust your app to tell you if your cycle is not normal,” Dr Copp and Dr Ford said.
