Consumer Health Info: Natural Cycles Fertility Awareness App


What is Natural Cycles?

Natural Cycles is the first smartphone application (“app”) for contraception cleared by the FDA. Natural Cycles is a high-tech version of the classic rhythm method (also called natural family planning or the fertility awareness method) in which users track their ovulation cycles in order to avoid pregnancy. It is one of several dozen fertility apps available for download in the US that uses personal health information uploaded by users to predict days on which it is and isn’t safe to have unprotected sex. It is marketed as a new, technology-based, and “100% natural” form of contraception. Natural Cycles does not prevent against sexually transmitted infections.

How Does It Work?

Natural Cycles combines data about your menstrual cycle and your daily basal body temperature to predict when you’re most likely to get pregnant.

Additional Information:

Your basal body temperature (BBT) is your baseline temperature when you’re completely at rest. It is measured by a special, more sensitive thermometer and should be your lowest temperature in a 24-hour period. BBTs are used in fertility tracking because there’s a slight increase in body temperature around ovulation.

Accurately recording your BBT is notoriously difficult because the temperature reading will change if:

  • You don’t take it immediately after waking up
  • You get out of bed before taking it, for example, to use the bathroom, get a glass of water, or because your thermometer isn’t within reach
  • You are sick or hungover
  • You sleep less or more than usual
  • You are traveling, especially to a different climate

The company stores data from your BBT readings and past cycles in its database. Then for a subscription fee, it crunches the numbers using a proprietary algorithm to make predictions about when you’re most likely to become pregnant. The app displays either a green “infertile” reading letting you know it’s safe to have unprotected sex or a red “fertile” reading warning you to abstain from sex or use a barrier method (like a condom). The app takes a conservative approach to assessing fertility and classifies indecisive temperature measurements as red/fertile by default. For someone with a regular period, the app shows red days from day 6 to day 16 of the menstrual cycle, on average. Natural Cycles is not a “stand-alone” contraceptive method. It must be paired with either abstinence or other methods of non-hormonal contraception on red days.

Natural Cycles brand influencers on social media promote the app but don't make its limitations clear. Waking up in the middle of the night to care for young children or pets can throw off your BBT.

It can take up to three months for the app to ‘learn’ your likely menstrual cycle. Natural Cycles’ maker claims the app is “effective from day one,” but that simply means that the app displays more red (use protection) days than green days until it has gathered enough data. On red days, you must either use a barrier method for protection or abstain from intercourse altogether.


While the National Women’s Health Network strongly endorses the kind of body knowledge and self-care which Natural Cycles and other fertility awareness apps can foster, we have strong concerns about the app’s ability to replace other forms of contraception for most people.

Highlighted Content Related To Birth Control:

Contraception Self-Advocacy

Comments Off on Contraception Self-Advocacy

Brightness Among the Clouds: Positive Women’s Health Efforts at the FDA

Comments Off on Brightness Among the Clouds: Positive Women’s Health Efforts at the FDA

Fighting for Contraceptive Coverage Without Copay

Comments Off on Fighting for Contraceptive Coverage Without Copay

Finding Birth Control Online: An NWHN Guide

Comments Off on Finding Birth Control Online: An NWHN Guide

Is the Pope in Charge of Your Hospital Bed?

Comments Off on Is the Pope in Charge of Your Hospital Bed?