Natural Cycles has become the first fertility app to be approved as a contraceptive in Europe. Its CE marking of class IIb signifies that it has met safety, health and efficacy requirements in the same risk category as a condom.

The app is based on natural family planning methods that existed long before smartphone apps ever did, but Natural Cycles modernizes those tracking methods by combining readings from a basal thermometer with a proprietary algorithm that accounts for cycle irregularities and sperm survival rates. It presents information in a mobile interface that denotes which days the user is not fertile and which days she should use protection.

One study of 317 women showed that the Natural Cycles algorithm was able to identify ovulation with near-ultrasound level accuracy. Another study, which was performed on over 4,000 women, showed that an average of seven women out of 100 became pregnant in a year when using Natural Cycles as a birth control method. Both studies were published in The European Journal of Contraception & Reproductive Health Care.

This is equivalent to a typical use Pearl Index (a measurement used in clinical settings to denote birth control efficacy) of 7.0. For reference's sake, traditional natural family planning is usually considered to have a typical use Pearl Index of 25. Typical use Pearl Index for the pill is usually reported around 9.

Natural Cycles is available on iOS and Android. It is a subscription-based service which starts at US$9.90 per month, or $5.80 per month for a yearly plan with a thermometer included.

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