The study, conducted by contraceptive app Natural Cycles and University College London, analysed data from more than 600,000 menstrual cycles and 124,648 women from the UK, Sweden and USA.
Data was collected from women aged between 18 and 45, who had a BMI between 15 and 50. It revealed that the woman’s average menstrual cycle actually lasts 29.3 days, with around 65 per cent of women’s cycles lasting between 25 and 30 days.
Remember when you started learning about periods as a pre-teen and the first thing you were taught was that cycles lasted 28 days? Well, it turns out your teachers were wrong and that isn’t strictly true. According to a new report, just 13 per cent of women have cycles that last exactly 28 days.
This revelation could prove particularly important for couples trying to get pregnant, as it highlights how fertility-tracking methods based on calendar dates alone could be misleading. “Our study shows that few women have the textbook 28-day cycle, with some experiencing very short or very long cycles,” said Professor Joyce Harper, from the UCL Institute for Women’s Health.
“We also demonstrate that ovulation does not occur consistently on day 14 and therefore it is important that women who wish to plan a pregnancy are having intercourse on their fertile days. In order to identify the fertile period, it is important to track other measures such as basal body temperature as cycle dates alone are not informative.”
So in case you were worried your cycles weren’t regular, don’t fret – it turns out most of them aren’t. And if you’re trying to get pregnant, invest in a thermometer to check your daily basal body temperature stat!