Why Natural Cycles Stands Out in Fertility Tracking and Hormone-Free Birth Control?

For most of modern history, women seeking birth control have been offered a version of the same basic trade: accept a pharmacological intervention and its associated side effects, or accept the uncertainty of older, less reliable non-hormonal methods. That binary held for decades. Not because better options were impossible, but because nobody had applied the same scientific rigour to the female cycle that the pharmaceutical industry had applied to hormonal intervention.

Natural Cycles was founded on the premise that a sufficiently intelligent algorithm, trained on the right data and validated to the same standards as any regulated medical device, could offer a third option: a hormone-free birth control method that is clinically proven, personalised to the individual, and accurate enough to have earned the trust of six million women worldwide. The fact that this app now holds FDA clearance, CE marking, and a 4.8-star rating across 58,000 App Store reviews suggests that premise was right.

Founded by a Physicist Who Searched for the Higgs Boson

The origin story of Natural Cycles is one of the more unusual in femtech. Dr. Elina Berglund Scherwitzl was a particle physicist at CERN, a member of the team that discovered the Higgs boson in a project that went on to win the Nobel Prize in Physics. After removing her own birth control implant, she found herself without a reliable, non-hormonal contraceptive option that met the scientific standards she expected. Rather than accepting that gap as a given, she did what particle physicists do: she built a model.

The fertility algorithm she developed, applying Bayesian statistical methods to basal body temperature data, became the foundation of Natural Cycles. Together with her co-founder and husband, Raoul Scherwitzl, she turned that algorithm into an app, launched it in Sweden in 2014, and spent the following years building the clinical evidence base that would earn it FDA clearance in 2018, making it the first and only software-as-a-medical-device to receive that designation as a contraceptive method.

“Natural Cycles plays a huge role in women’s lives, which humbles us. So we always have their best interest at heart in every decision we make.”  – Dr. Elina Berglund Scherwitzl, Co-founder and CEO, Natural Cycles

How Natural Cycles Works: Three Steps, One Daily Habit

The core mechanic of Natural Cycles is elegant in its simplicity, even though the science underneath it is anything but. Each morning, a user measures her basal body temperature, the resting temperature of the body before any activity, using a thermometer, a compatible wearable, or the NC° Band, the company’s own dedicated tracking device launched in 2025. That measurement is logged in the app, and the NC° algorithm processes it alongside cycle history, ovulation patterns, and other tracked factors to determine the user’s fertility status for that day.

The result is displayed as one of two states: a Green Day, indicating the user is not in her fertile window and can have unprotected sex without risk of pregnancy, or a Red Day, indicating she is fertile or the algorithm requires more data before it can assign a non-fertile status confidently.

The algorithm that produces this status is not a static calendar calculation. It accounts for the individual user’s specific cycle length, ovulation day variability, temperature baseline, and cycle-to-cycle irregularity. Because body temperature rises measurably after ovulation due to the influence of progesterone, the NC° algorithm can detect the post-ovulatory thermal shift and confirm that ovulation has occurred, which is the biological event that determines the fertile window. This makes Natural Cycles meaningfully different from calendar-based methods like the rhythm method, which use historical averages to predict future fertile days without being able to confirm ovulation has happened.

One App, Five Modes: The Full Fertility Journey

What has made Natural Cycles genuinely distinctive in the femtech landscape is its evolution from a single-purpose contraceptive tool into a comprehensive platform for reproductive health across an entire lifetime. The app now operates across five distinct modes, each purpose-built for a different stage of a woman’s fertility journey, and each powered by the same underlying NC° algorithm architecture.

• NC° Birth Control is the foundational product: the FDA-cleared contraceptive mode that uses daily temperature and cycle data to identify fertile and non-fertile days.
• NC° Plan Pregnancy flips the same system to help users identify their fertile window when trying to conceive, using the algorithm to pinpoint the days with the highest probability of conception rather than avoiding them.
• NC° Follow Pregnancy guides users through an active pregnancy with week-by-week tracking and health information.
• NC° Postpartum, introduced in 2024, addresses the specific physiological context of recovery after childbirth, a period during which hormonal and cycle patterns are highly variable and standard tracking approaches are unreliable.
• NC° Perimenopause, launched in 2025, is the most recent and arguably most ambitious addition: the first app mode powered by a dedicated NC° Menopause Algorithm, designed to help users navigate the hormonal shifts, cycle irregularities, and symptom patterns of perimenopause, including for those using hormone therapy or hormonal birth control, who cannot use the app as contraception but can use it for symptom tracking and cycle insights.

The Perimenopause mode in particular addresses a gap that the broader digital health market has been slow to fill. Women experiencing perimenopause are navigating a transition that can last anywhere from a few months to over a decade, during which their cycles become unpredictable, their symptoms can be disorienting, and their access to useful data-driven guidance has historically been minimal. NC° Perimenopause tracks hot flashes, brain fog, joint pain, vaginal dryness, heart palpitations, and fatigue alongside lifestyle factors that may trigger or relieve symptoms, producing a Cycle Report that users can bring to their healthcare provider to support more personalised treatment decisions.

Check out what Dr. Magda Armbruster, Head of Product at Natural Cycles, has to say on Femtech and AI

The Science That Makes Natural Cycles More Than an App

The credential that separates Natural Cycles from the substantial and growing category of fertility tracking apps is its status as a regulated medical device. FDA clearance and CE marking are not marketing designations. They are the outcome of a regulatory process that required Natural Cycles to demonstrate, through a prospective clinical study of over 22,000 women, that its algorithm achieves 93 percent typical use effectiveness and 98 percent perfect use effectiveness as a contraceptive method. These are the same standards applied to physical contraceptive methods.

The algorithm must be conservative enough that it will not assign a Green Day status unless the statistical confidence in a non-fertile state is high enough to meet clinical requirements.

The research programme that underlies this regulatory status is ongoing. Natural Cycles has published 28 peer-reviewed studies in collaboration with leading academic institutions and healthcare providers, covering topics from cycle variability and ovulation patterns to the relationship between basal body temperature and broader health markers.

This commitment to published, independently reviewable science is a deliberate strategic choice: in a category where unregulated apps make implausible claims, the peer-reviewed literature is the clearest signal of the difference between a wellness product and a medical device.

Compatible With How You Already Live: Wearables and Device Integration

One of the most practical improvements in Natural Cycles’ recent development has been its expansion of compatible device integrations. The original product required a standard oral thermometer and manual temperature entry each morning. While this remains a valid and clinically effective measurement method, the addition of wearable integrations has substantially reduced the friction of daily use and improved the consistency of data collection. Compatible Devices:

• Oura Ring
• Apple Watch
• Garmin Watch
• NC° Band
• Standard Basal Thermometer

Natural Cycles launched the NC° Band in 2025, its own dedicated wearable designed specifically for overnight temperature tracking. Unlike general-purpose smartwatches that measure skin temperature as one of many health metrics, the NC° Band is purpose-built for the basal body temperature measurements that the NC° algorithm requires, offering a dedicated hardware option for users who want maximum measurement accuracy and seamless app integration without relying on a third-party device. Critically, the app’s contraceptive effectiveness remains constant regardless of which measurement device is used, a point that Natural Cycles is explicit about: the algorithm’s clinical validation applies to all supported measurement methods.

Privacy Built Into the Product, Not Bolted On

For an app handling some of the most sensitive health data a person can generate, reproductive status, pregnancy intentions, and cycle patterns, the privacy architecture is not a compliance afterthought. It is a core product feature. Natural Cycles’ approach to data privacy is organised around two key innovations.

• NC° Secure: A comprehensive data protection programme covering encryption, cybersecurity protocols, GDPR compliance, and regular third-party audits. Reproductive data is handled to standards that exceed most consumer health apps given the medical device regulatory requirements the company operates under.
• Go Anonymous Mode: A unique privacy feature that allows users to completely separate their identity from their fertility data. In Go Anonymous mode, not even Natural Cycles can link the data back to the user. Identity and health data are structurally decoupled rather than simply stored separately.
• Subscription Model: Natural Cycles is funded by subscriptions, not by data monetisation. Because the business model does not depend on selling user data to advertisers or third parties, the product can be designed with privacy as its genuine priority rather than a constraint on revenue.
• NC° Partner View: An optional feature that lets users share their fertility data with a partner on a separate device. Controlled entirely by the user: multiple accounts can be added and access removed at any time. Built for the user first, shared only by choice.

Natural Cycles (NC°) is Available on App Store and Google Play

Natural Cycles is available as a subscription-based app on both iOS and Android, accessible in more than 35 countries and offered in 15 languages. The app is effective from day one, even for users with irregular cycles, and does not require a monitoring period before it can be used as contraception. Users who already own a compatible wearable can begin measuring immediately upon sign-up. New users can access exclusive discounts on supported devices through the app.

The trajectory of Natural Cycles from a physicist’s personal project in 2013 to a globally regulated medical device trusted by six million women is, in the broadest sense, a story about what happens when the standards of particle physics are applied to a problem that the pharmaceutical industry had decided was too complex to solve without hormones. As Dr. Elina Berglund Scherwitzl’s former colleagues at CERN learned, complexity is not a reason to stop looking for a signal. It is a reason to build a better model.