Culture and menstruation the ideal of synchronised tidal, lunar, menstrual and seasonal periodicities whose overall harmony (it is believed) confers spiritual power and fertility. To many, such cultural associations appear persuasive in view of the fact that in humans, the menstrual cycle quite closely approximates the moon's 29.5-day synodic cycle, unlike in chimpanzees (~36 days) or bonobos (~40 days). Statistical information from hunter gatherers is lacking, but where large-scale western studies focus on women's peak reproductive years—removing outlier values—the cycle length gravitates around 29.1–29.5 days, while the figure for women in their thirties shortens toward 28 days. In no extant human population has
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.