Guides to periods, ovulation and the menstrual cycle. Lunation is a private period, ovulation and pregnancy tracker for iPhone. It predicts your next period and fertile window, works without an account, and never shares or sells your health data.https://lunation.meenhttps://lunation.me/learn/are-period-tracking-apps-privatehttps://lunation.me/learn/are-period-tracking-apps-privateIt depends on the app. In the US, HIPAA generally does not cover health data you enter into a consumer app, so privacy rests on each company's own policy, and some trackers have shared sensitive data with analytics and ad firms. Before logging, check whether an account is required, whether data is sold or shared for ads, what the App Privacy label lists, and whether you can delete everything.Tue, 10 Nov 2026 00:00:00 GMTHealth data privacyhttps://lunation.me/learn/how-long-is-a-normal-menstrual-cyclehttps://lunation.me/learn/how-long-is-a-normal-menstrual-cycleFor most adults, a menstrual cycle lasts 21 to 35 days, counted from the first day of one period to the day before the next, according to ACOG and the NHS. The average is about 28 days, yet only around 13% of cycles are exactly that long. In the first years after periods start, cycles of 21 to 45 days are common.Tue, 10 Nov 2026 00:00:00 GMTMenstrual cyclehttps://lunation.me/learn/how-to-predict-your-next-periodhttps://lunation.me/learn/how-to-predict-your-next-periodAdd your average cycle length to the first day of your last period. If your last period started on March 3 and your cycles average 29 days, your next one is likely around April 1. Base the average on at least three recent cycles, and expect a window of a few days, because most people's cycles vary a little each month.Tue, 10 Nov 2026 00:00:00 GMTPeriodshttps://lunation.me/learn/what-are-the-phases-of-the-menstrual-cyclehttps://lunation.me/learn/what-are-the-phases-of-the-menstrual-cycleThe menstrual cycle has four phases: menstruation (your period, usually 2 to 7 days), the follicular phase (from day 1 until ovulation, as estrogen rises and an egg matures), ovulation (an LH surge releases the egg, around day 14 of a 28-day cycle) and the luteal phase (progesterone rises for roughly 12 to 14 days until the next period).Tue, 10 Nov 2026 00:00:00 GMTMenstrual cyclehttps://lunation.me/learn/signs-of-ovulationhttps://lunation.me/learn/signs-of-ovulationThe clearest signs of ovulation are clear, slippery, stretchy cervical mucus in the days before it, a positive LH (ovulation) test, after which ovulation usually follows within 24 to 36 hours, and a small rise in resting body temperature afterwards. Some people also notice one-sided pelvic twinges, tender breasts, bloating or a higher sex drive. Many notice no signs at all.Tue, 10 Nov 2026 00:00:00 GMTOvulation & fertile windowhttps://lunation.me/learn/when-am-i-most-fertilehttps://lunation.me/learn/when-am-i-most-fertileYou are most fertile during the six days that end on the day you ovulate, and the best odds fall in the last three: the two days before ovulation and ovulation day itself. In a 28-day cycle that is roughly days 9 to 14. Ovulation moves with cycle length, though: it usually happens 10 to 16 days before your next period, not on a fixed day.Tue, 10 Nov 2026 00:00:00 GMTOvulation & fertile window