Natural Cycles

Natural Cycles is an FDA-cleared birth control app that uses basal body temperature (BBT) data and an AI-powered algorithm to determine daily fertility status. Developed by the Swedish company Natural Cycles AB, the app is designed for women who want a hormone-free approach to family planning. It serves two primary use cases: preventing pregnancy and planning pregnancy. The app pairs with a thermometer to track temperature shifts that signal ovulation, giving users a daily green (not fertile) or red (fertile) reading.

How Natural Cycles works

Each morning, the user takes her basal body temperature before getting out of bed and logs it in the app. The AI algorithm analyzes temperature patterns over time, learning each user’s unique cycle to identify the fertile window. On green days, the algorithm has determined that pregnancy is unlikely. On red days, the user is potentially fertile and should use protection or abstain to avoid pregnancy.

The algorithm improves its accuracy the longer it collects data. In the first few cycles, users typically see more red days as the system calibrates. Over time, as the algorithm builds a clearer picture of the individual cycle pattern, green days generally increase. The app also provides ovulation detection and period prediction based on the accumulated temperature data.

Natural Cycles sells its own Bluetooth-connected thermometer, though users can also log temperatures manually from a standard BBT thermometer. The connected device syncs readings automatically, which reduces the chance of input errors.

Strengths

• FDA clearance. Natural Cycles is the first and, as of this writing, only FDA-cleared app for contraception in the United States. That regulatory status sets it apart from general period trackers that may offer fertility predictions but lack clinical validation for birth control use.
• Hormone-free method. For users who experience side effects from hormonal contraception or simply prefer not to use it, the app provides a non-invasive alternative grounded in physiological data rather than synthetic hormones.
• Personalized algorithm. The AI does not rely on population averages alone. It adapts to individual cycle patterns, which means predictions become more tailored over the first several months of use.
• Dual-purpose design. The same temperature tracking and algorithm that help prevent pregnancy can be switched to “plan pregnancy” mode, making the app useful across different life stages.
• Simple daily routine. The core commitment is a single temperature reading each morning. There are no injections, no device insertions, and no pharmacy visits.

Limitations

• Requires consistent daily measurement. The app depends on a temperature reading taken at roughly the same time each morning, before physical activity. Irregular sleep schedules, shift work, or frequent travel across time zones can reduce data quality and lead to more red (uncertain) days.
• Less effective than some alternatives. With typical use, fertility awareness methods have higher failure rates than hormonal IUDs, implants, or oral contraceptives. Users need to be comfortable with that trade-off and disciplined about following the red-day and green-day guidance.
• Slow calibration period. The algorithm needs at least one to three full cycles of data before it can provide reliable predictions. During that ramp-up phase, expect a higher proportion of red days, which can feel restrictive.
• External factors affect readings. Alcohol consumption, illness, poor sleep, and certain medications can elevate basal temperature and skew the data. The app allows users to flag these days, but frequent disruptions reduce the algorithm’s confidence.
• Ongoing cost. At $12.99 per month plus the cost of a thermometer, the subscription adds up over time. Users should weigh this against the one-time or lower recurring cost of other contraceptive methods.

Who it is for

Natural Cycles fits best for women with relatively regular cycles who want to avoid hormonal birth control and are willing to commit to a daily morning routine. It suits users who are comfortable with a method that requires active participation rather than a set-and-forget device. Women in the planning-pregnancy phase can also benefit, since the same cycle data that prevents conception can help identify optimal timing for it. It is less ideal for anyone with highly irregular cycles, inconsistent sleep patterns, or a low tolerance for the higher typical-use failure rate compared to long-acting contraceptives.

How it compares

Natural Cycles occupies a specific niche as an FDA-cleared contraceptive app, which separates it from general health and wellness trackers. Flo Health is a widely used period and ovulation tracker that offers cycle insights and health content, but it is not cleared as a contraceptive device. Users who want detailed cycle tracking without the birth-control claim may find Flo Health sufficient. For users whose interest in health AI extends beyond reproductive health into stress management and mental wellness, Headspace covers meditation and mindfulness, a complementary but entirely different category. Natural Cycles stands alone among these options in offering a clinically validated, algorithm-driven contraceptive method built on daily temperature data.