For a woman using Natural Cycles, the daily routine involves just 3 steps:

  1. After waking and before getting up, she measures her temperature in the mouth, in the posterior sublingual pocket with a two decimal basal thermometer until the thermometer beeps, which takes less than 1 minute
  2. She enters her temperature data into the app (via mobile phone). She must also enter her menstruation dates each month and can input luteinising hormone (LH) test data, but this is optional.
  3. She checks her fertility: Green = Not fertile (no need for protection during intercourse), Red = fertile (need for protection during intercourse)


The algorithm adapts to every woman’s unique cycle pattern by learning over time as she adds more data. The number of green days rises accordingly. Regular measuring (at least 5 times a week), a steady temperature and a regular menstrual cycle all contribute to an increased allocation of green days. 1  

If temperature measurements are not taken regularly, the algorithm will give the user more red days. The following factors may also increase the number of red days returned:

  • Having recently stopped hormonal contraception
  • Highly irregular cycles
  • Atypical fluctuating temperatures 2

1Berglund Scherwitzl E, Lindén Hirschberg A, Scherwitzl R. Identification and prediction of the fertile window using NaturalCycles. The European Journal of Contraception & Reproductive Health Care. 2015;20(5):403-408.
2E.g. due to medical conditions (thyroid) or lifestyle (irregular sleep (+/- 2 hours than normal)), use of certain medication, a hangover from extensive alcohol consumption, insomnia, smoking or drugs, an infection or feeling ill, or working a night shift.

Downloadable files

Patient brochure