F.A.Q. How Does Flo Define Days Favorable for Conception? If a woman can become pregnant only during ovulation, why is the fertile window much wider? The app includes additional parameters to help you calculate your fertile window length. For example, your ovulation is in 5 days and today you’ve had unprotected sex. Your egg could be fertilized, because sperm can survive for up to 5 days inside a woman’s body. Usually, ovulation is hard to predict with 100% accuracy. (Only a doctor in the clinic can indicate it correctly with the help of an ultrasound.) However, if you continuously input information about your cycles and symptoms into Flo, the app can give you an accurate fertile window. You can also track your basal body temperature. The app makes predictions automatically and shows wide fertile window as trying to consider all the possible combinations. Updated on November 29, 2018 Read this next F.A.Q. How Will Flo Help Me Get Pregnant? F.A.Q. Why Should I Track My Cycle If I Don’t Plan to Conceive?