MORE than one in five women are unable to report their menstrual cycle length, a 2026 UK-based retrospective, cross-sectional analysis has found.
Substantial gaps in self-awareness were observed across the cohort, but the highest levels of uncertainty were reported by women under 25-years-old, one in three of whom did not know their cycle length.
Menstrual Cycle Awareness and Reproductive Health
Menstrual cycle awareness is a critical, often overlooked, component of reproductive health. It helps individuals recognise cycle changes and seek medical care when necessary.
Low menstrual cycle awareness can contribute to misconceptions, stigma, and delays in healthcare management.
Fewer than one in five women in England said they have sufficient information on menstrual wellbeing, according to the UK women’s health strategy survey.
Trends in Menstrual Cycle Awareness
The study analysed a sample of more than 383,000 participants aged 18-50-years-old. It examined self-reported data collected between September 2020 and January 2025, via an online health assessment. It revealed substantial gaps in understanding of personal cycle characteristics.
Overall, 22.2% of participants reported they did not know their cycle length. This figure rose to 33.4% in under 25-years-olds. Uncertainty then decreased with aged to 15.9% among those aged 36-40-years-old, before increasing slightly to 19.4% among participants aged 45-years-old and above.
Awareness of period length was generally higher than cycle length, with 9.5% unable to report. Under 25-years-olds still showed the highest unawareness, which rose to 13.8% among the relevant demographic.
Participants under 25-years-old were also more likely to report cycle lengths outside the clinically regular 21–35-day range, despite describing their menstrual cycles as regular. This reflected a discordance between perceived cycle regularity and reported cycle length.
Self-Reporting of Menstrual Cycle Awareness
Reliance on self-reported data means that recall bias could give rise to inaccuracies in reported cycle characteristics. Participants were also self-selected. Many may have previously been identified or suspected a menstrual health concern prior to testing. Hence, the cohort was likely to be more self-aware than the general population, limiting generalisability.
The online health assessment was not clinically validated as a comprehensive assessment of menstrual health knowledge, meaning that responses represented self-reported perceptions over objective knowledge.
Clinical Learnings
Researchers submitted that a clear framework for interpreting menstrual patterns, particularly in early adulthood, is lacking. They called for the entrenchment of menstrual cycle awareness as a core component of lifelong health, rather than framing it as fertility-focused.
Menstrual education, engagement with healthcare services, and accurate and ethical digital health tools could support earlier recognition of abnormalities, promoting reproductive health.
References
Ali Z E et al. How well do women understand their menstrual cycles? Insights from 282,085 UK based women. Reprod Health. 2026;DOI:doi.org/10.1186/s12978-026-02275-3
GOV.UK. Results of the ‘women’s health – let’s talk about it’ survey. 2022. Available at: https://www.gov.uk/government/calls-for-evidence/womens-health-strategy-call-for-evidence/outcome/results-of-the-womens-health-lets-talk-about-it-survey. Last accessed 9 February 2026.
