Validation of Effectiveness on NaturalCycles Users

Inclusion Criteria: * Wants to avoid pregnancy for 13 cycles. * Is willing to rely solely on Natural Cycles as their sole contraception method for 13 cycles. * Is not currently using permanent contraceptive methods, such as sterilization (of either the user or their partner), or hormonal methods, such as the hormonal contraceptive implant or IUD. * Has an intact uterus, both ovaries and both fallopian tubes to the best of their knowledge. * Has an average cycle length between 21 and 35 days. The user anticipates heterosexual intercourse at least once a month in the next year. * Is willing to enter data on a daily basis and perform pregnancy tests as requested by protocol. * Is willing to complete a satisfaction survey at the end of her study participation. Exclusion Criteria: * Has EU-citizenship * Has had a Depo-Provera injection in the last 10 months or has had less than three consecutive, spontaneous menstrual cycles since their last injection. * Has had less than three consecutive, spontaneous menstrual cycles after removing a hormonal implant. * Has had less than three consecutive, spontaneous menstrual cycles after the end of a pregnancy. * Has had less than three consecutive, spontaneous menstrual cycles since she last breastfed. * Has (or partner has) known fertility issues, such as infertility and sterilization, or have been advised by a healthcare professional that they may have difficulty conceiving for any reason. * Has a medical condition possibly impacting fertility, i.e. endometriosis, a history of Pelvic Inflammatory Disease (PID), significant uterine fibroids or adenomyosis, or another diagnosed medical condition that they have been told affects fertility. * Is regularly taking one of the following prescribed pharmaceutical medications known to be teratogenic (i.e., a medication that can cause birth defects): Isotretinoin (like Accutane, Absorica, Claravis, or Myorisan) for severe acne Valproic acid or divalproex sodium (like Depakote, Depakene, or Topamax) for seizures (epilepsy), migraines, or bipolar disorder Methotrexate (Trexall, Rheumatrex) or leflunomide (Arava) for autoimmune conditions ACE Inhibitors (like Lisinopril, Enalapril) or Angiotensin II Receptor Blockers (ARBs) (like Losartan, Valsartan) for high blood pressure or heart conditions Warfarin (Coumadin, Jantoven) for blood clot prevention