How do we really know? My cycle has been odd since 40 (heavy flow, more unpredictable cycles, menstrual migraines) but now at 48 it’s really getting weird (2 periods in a month weird). My gyn says that means perimenopause is probably just starting for me. In addition to other tests to rule out scary stuff, I just had some hormonal testing and she confirmed I’m perimenopausal. She’s saying I’ll be menopausal in like 4 years.