Natural Cycles° on Instagram: "She really said she’s here for one day & one day only 🥚💅 Sperm can survive up to five days in the female reproductive system, so Natural Cycles needs to take sperm survival into account to work effectively at finding your fertile and non-fertile days. The fertile window is six days long if the sperm encounters the right environment in the vagina, uterus, and fallopian tubes. Follow the link in our bio to learn more about how Natural Cycles takes sperm survival in