Missing temperature readings will not affect Natural Cycles’ effectiveness as birth control. The algorithm is designed to prioritize safety and will always adjust for missing data. If the algorithm lacks sufficient temperature data to safely confirm that you are not fertile on a given day, that day will be colored Red (meaning you must use protection or abstain).
If you skip a lot of temperatures, this will make it harder for the algorithm to identify your fertile window. As a result, you will get more Red Days (for NC° Birth Control) or Brown Days (for NC° Plan Pregnancy), which may reduce your overall satisfaction with the app.
We recommend adding at least five temperatures per week to get the maximum number of Green Days and help the algorithm narrow down your ovulation window as precisely as possible.
Struggling with a Basal Thermometer?
If you use a basal thermometer and find it difficult to remember to measure immediately upon waking, consider switching to one of our approved wearable devices. When using Natural Cycles with a wearable device, your temperature data is automatically measured overnight while you sleep. To explore this option, see our guide: Which device is right for me?
You may also find these tips helpful for your current routine: How to remember to measure your temperature with a basal thermometer.