1 in 4 women don’t know this ‘fundamental’ fact about their periods

Hertility’s report includes data and insight collected from thousands of women across the UK & Ireland (Picture: Getty Images) A recent survey of more than 383,000 UK women aged 18 to 50 has revealed just how little many of us know about our own menstrual cycles. The research, published by data-driven women’s health platform Hertility, draws on seven years of data, more than half a million health assessments and the lived experiences of hundreds of thousands of women. Its findings expose a worrying gap in menstrual health knowledge: nearly one in four (22%) respondents did not know their menstrual cycle length. This figure rises to one in three among those ages under 25. Meanwhile one in 10 could not accurately say how long their period lasted. Ask Metro Use AI to go deeper into the stories you care about – powered by Metro and trusted publications. This may come as a surprise to some, especially given that a YouGov poll in March 2024 found that 51% of women aged 44 and under use an app or device to monitor their cycles. But logging your period on an app doesn’t mean we necessarily understand the fundamentals of what’s going on in our body. Dr Helen O’Neill, CEO of Hertility and associate professor in reproductive and molecular genetics at UCL, warns that it’s this disconnect, fuelled by a serious lack of education on the menstrual cycle, that means red flags regarding health concerns consistently go unchecked. Do you know your menstrual cycle well? (Picture: Getty Images) ‘Right now, a woman’s cycle lives in one app, her symptoms in another and her hormone results somewhere else,’ Dr O’Neill explains. ‘Each gives her a fragment of information, but not the whole picture, and the burden of interpreting it all has quietly shifted from healthcare systems onto women themselves.’ It’s almost as though we’ve been presented with a complex system, but given no proper instructions on how it works. It should be noted that this isn’t the first time women in the UK have spoken out about not feeling confident when it comes to understanding their own body. In February 2025, another nationwide survey discovered that only one in 10 women could correctly identify all the signs of heavy menstrual bleeding. Metro spoke with Dr O’Neill to understand exactly why this disconnect exists – and why it’s so important we close the gap. One of the most popular period tracking platforms, Flo, has over 77 million users worldwide (Picture: Getty Images) Why do so many women know so little about their cycle? Dr O’Neill wants women to be ‘as familiar with the phases of their menstrual cycle as they are with the days of the week.’ Yet women of all ages, including those in their 50s and 60s, still ask her: ‘Why was I never taught the basics about my own body?’ ‘Your menstrual cycle is incredibly powerful because it governs how we operate as women,’ she tells Metro. ‘Our hormones are responsible for our skin, our mood, our appetite, our metabolism, our sleep, our energy, our sex drive, every facet of our lives is governed by these key hormones and those hormones are changing in every single day of every single month,’ she explains. But as a society, we’re simply not given the education to equip ourselves properly. A 2024 study led by the University of Bristol and Anglia Ruskin University found that many young women left school lacking basic menstrual health knowledge – with 62.4% rating their education as ‘poor’ or ‘very poor’ at preparing them to manage their periods. Period education in the UK may have got better on paper, but it’s still massively lacking (Picture: Getty Images) There’s also another factor. For a lot of women, Dr O’Neill explains, ‘the closest menstrual education that you’re going to get is going to be from your mum, your sister, or your aunt. ‘And if your mum, sister, and aunt all suffer, but have never been also taught about their own cycles, then you will learn that if your mum has really heavy, painful periods, then that is just what it is to have a period. ‘You almost inherit the acceptance.’ As part of the report, Hertility asked 45,000 women about their journey to a PCOS diagnosis and found that a significant proportion had ruled themselves out of seeking care. For many, this was because they did not believe their symptoms were serious enough to warrant further investigation. Why is it so important to know the length of your cycle? Out of the 383,000 UK women aged 18 to 50 who completed Hertility’s online health assessment, the majority (67.4%) fell within the ‘clinically regular’ 21 to 35 day range. Yet for years, medical textbooks have taught that the ‘average’ menstrual cycle lasts 28 days. It might not be immediately obvious, but there’s a reason why it’s important you know exactly how your own cycle operates. Dr O’Neill explains that the main things to look at are the time between periods, how long the bleeding lasts and how heavy it is. ‘For example, count from the first day of one period to the first day of the next. Is it 25 days? Is it 32? Shorter? Longer? The same goes for the length of the bleed – if it’s too short or too long, it could be a sign that something isn’t right.’ Learning more about your period could help you reach a quicker diagnosis (Picture: Getty Images) There are four phases of menstruation, and your body requires certain amounts of each hormone to get through each of those phases. So, if one of those phases is short, or absent, or you’re bleeding too much, it’s an indication that your hormones may be off-balance. Irregularities can point to a number of things such as ovulation problems, thyroid dysfunction, PCOS and a range of other conditions. There’s also the fertility window. Hertility’s report found that 41% of women actively trying to conceive could not accurately identify their fertile window. This means that four in ten women were trying for a baby without knowing when their bodies were most ready to conceive. Do you know how long your menstrual cycle is? I could take a guessCheck Sign up to Metro's The Slice newsletter for your guide to what's on in London, with trusted reviews, offers and giveaways. For Dr O’Neill, she’s hoping this report will encourage women to feel empowered to not only understand how their body works, but to talk about it openly. One of the biggest barriers, she argues, is the language we use. Even common terms such as ‘menstrual waste’ and ‘sanitary products’ can reinforce the idea that periods are something shameful. ‘The words we use to describe female bodies contributes to a societal taboo around talking about our reproductive function. ‘It’s also a very insidious way of planting a seed at an early age. In many ways, you’re telling a young girl that she’s not clean. ‘But then I think women’s bodies have always been weaponised. They’re only ever spoken about when we’re trying to improve them.’ Do you have a story you’d like to share? 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