Clearblue & Natural Cycles Birth Control Kit is hormone-free and 93% effective with typical use[1]. The NC Birth Control app uses an algorithm to identify your fertile days (when you are most likely to get pregnant) based on basal body temperature. Your hormones cause your body temperature to rise after ovulation. This helps to identify where you are in your cycle. Simply measure your temperature when you wake up using the digital basal thermometer included in the starter pack, then add your reading to the NC app. The app calculates your fertility status for that day. Green Days (‘Not fertile’) mean you can have sex without protection[1]. Red Days (‘Use protection’) indicate you are likely to be fertile and at risk of getting pregnant. On Red Days you should use protection (such as condoms) or abstain from having sex to avoid pregnancy. If you’re using this method, it’s important you feel comfortable doing this and that you understand it does require a routine, including taking your temperature in the morning. Measuring your temperature once a day, on as many days as possible, allows the algorithm to quickly get to know your cycle. Aim to measure your temperature at least 5 days a week. On the days you use a Clearblue Digital Ovulation Test, add the result to the NC app. Clearblue Digital Ovulation Tests (15 tests and a digital holder also included in the starter pack) identify the surge in luteinizing hormone which happens 24-36 hours before ovulation, to pinpoint your most fertile days. Clearblue Digital Ovulation Tests are also sold separately as a refill pack (with holder). [1] Natural Cycles is 93% effective with typical use which means if 100 women use this method for 1 year, we expect 7 will become pregnant. Typical use includes all unintended pregnancies, such as due to having unprotected sex or using withdrawal on a Red Day, as well as pregnancies that occur while the method is used as intended.