Timing. Menopause is a single event in time after which a women, due to a cessation in ovarian function, experiences no further menstrual cycles. Post menopause are the years after this event and perimenopause is the time prior to this event -frequently associated with irregular and missed cycles and hot flashes.
Number of good eggs. Perimenopause (straw criteria) is when your period changes by more than 7 days (early) or when you go 60 days without a period (late). Menopause is 12 months without a period. It goes back to how many good eggs are left in your ovaries, each follicle or baby egg has cells around it which make estrogen and progesterone, the hormones which affect your cycle, thermostat, and moods.