Abstract Study question Do individuals who self-reported “suspected perimenopause” in health assessments meet the diagnostic criteria for perimenopause, menopause or premature ovarian insufficiency (POI) based on clinical guidance? Summary answer Users were likely to experience more mood symptoms, compared to vasomotor symptoms or cycle irregularities and only 5.5% met the NICE perimenopause diagnostic criteria. What is known already An estimated 13 million individuals are currently experiencing perimenopause or menopause in the United Kingdom. The recent surge in media attention, while helpful in fostering awareness, may also carry the unintended consequence of leading individuals to self-identify with perimenopause without a clear understanding, due to the historical gap in comprehensive education on the subject. This study aims to investigate the prevalent symptoms reported by individuals who self-reported suspected perimenopause in a health assessment and assess whether these individuals meet diagnostic criteria for perimenopause, menopause or premature ovarian insufficiency (POI) based on clinical guidance. Study design, size, duration In this retrospective observational study, data was analysed from 13,932 users approaching women’s health testing services, citing “I think I am perimenopausal” as their reason for using the service between August 2022 and January 2024. We analysed data on age, menstrual cycle characteristics and symptoms self-reported via an online health assessment. A sub group analysis, done on 891 users aged 21-58, also analysed serum follicle-stimulating hormone (FSH) measured via immunoassay using a capillary blood sample. Participants/materials, setting, methods Among the 13,932 users, 8,101 (58.1%) were <40 years old, 4,947 (35.5%) were aged 40-45 and 884 (6.3%) were >45 years old. The dataset was compared with NICE criteria, stating that perimenopause/menopause is diagnosed in women >45 experiencing cycle irregularities and vasomotor symptoms, with the addition of two FSH measurements >30 IU/L to diagnose perimenopause/menopause or POI in those <45 or < 40 respectively. Main results and the role of chance The most frequently reported symptoms were fatigue 10,434 (74.9%), anxiety 8,526 (61.2%), irritability 8,361 (60.0%), depression 8,280 (59.4%), brain fog 7,898 (56.7%), headaches 6,483 (46.5%), hot flushes 5,289 (38.0%), hair thinning/loss 5,224 (37.5%), feeling cold often 4,999 (35.9%), night sweats 4,939 (35.5%), vaginal dryness 3,595 (25.8%) and pain during intercourse 3,525 (25.3%). In terms of menstrual cycle regularity, 7,515 (53.9%) had regular periods, 4243 (30.5%) selected irregular periods, 956 (6.9%) selected ‘I’m not currently/no longer getting periods’, 1195 (8.6%) selected ‘I don’t get periods because of contraception/HRT’. The subgroup analysis found that among users <40 years old, 1.2% (n = 6/524) would potentially fit the POI diagnostic criteria based on a single FSH measurement >30 IU/L, vasomotor symptoms and cycle regularity. Based on the same criteria, 2.9% (n = 8/279) of users aged 40-45 would be diagnosed with perimenopause/menopause and 39.8%(n = 35/88 ) of users >45 years old met the perimenopause/menopause criteria. However, of the total, only 5.5% (n = 49/891) of individuals who self-identified as perimenopausal met the NICE diagnostic criteria. Limitations, reasons for caution The online health assessment collects self-reported data, potentially influencing results. Subgroup analysis included individuals with at least 1 FSH test, however, guidelines advise 2 consecutive high FSH levels for perimenopause diagnosis, possibly reducing the number eligible for a potential perimenopause diagnosis. Wider implications of the findings Our data suggests users are most likely to experience mood symptoms, compared to vasomotor symptoms or cycle irregularities, which are required for a diagnosis. This spotlights the importance of including patient voices in clinical guidelines and the need for improved public awareness regarding perimenopause to promote healthcare-seeking behaviour for symptoms. Trial registration number NA