Inclusion Criteria:  Female Aged 18 to 45 years Menstrual cycles are 21-60 days long Seeking to predict when her next period will start Seeking to give informed consent and comply with the investigational procedures Has a compatible iPhone with internet access that they are willing to use for the study (iPhone 7+ and iOS 13 and above)  Exclusion Criteria:  Currently pregnant or breastfeeding Used Clearblue® me (Period Tracker app), Persona Contraception Monitor or Clearblue Advanced Fertility Monitor within the last six months Currently or previously employed by SPD, Abbott, Alere, Unipath, P&G or affiliates Has an immediate* relative currently or previously (within past 5 years) employed by SPD, Abbott, Alere, Unipath or P&G, or affiliates Is a qualified or trainee healthcare professional (HCP) Has professional experience of using dipstick type tests or lateral flow devices Using any treatment which may affect the menstrual cycle (e.g. contraceptive pill) Using hormone replacement medications containing LH or hCG (e.g. Pregnyl®) Is currently seeking to conceive Has been diagnosed with polycystic ovarian syndrome (PCOS) Has PCOS symptoms e.g. very irregular cycles, hirsutism *Immediate relatives are defined as parents, children, siblings or partner/spouse