Menstrual cycle shortest and longest cycle lengths is considered very irregular. The average menstrual cycle lasts 28 days. The variability of menstrual cycle lengths is highest for women under 25 years of age and is lowest, that is, most regular, for ages 25 to 39. Subsequently, the variability increases slightly for women aged 40 to 44. The luteal phase of the menstrual cycle is about the same length in most individuals (mean 14.13 days, standard deviation 1.41 days) whereas the follicular phase tends to show much more variability (log-normally distributed with 95% of individuals having follicular phases between 10.3 and 16.3 days).
Menstrual cup spillage. During peak flow, most women use two disposable cups per day. Reusable menstrual products (including menstrual cups, but not disposable menstrual cups) are more economical than disposable products. Money will be saved using a menstrual cup, compared with other options such as tampons. A woman in a developed country spends an average of US$60 per year on pads and tampons. If a woman menstruates for 40 years, the lifetime expense for pads and tampons is US$2,400. If the average silicon menstrual cup lasts between one and five years, then between eight and 40 would be needed in 40 years.