Our mission at Body Freedom relies on support from readers like you. We fairly compensate our expert writers and conduct thorough product evaluations monthly, incurring significant costs. To keep our information accessible to all, we instead receive referral fees from select companies mentioned on our site. Here's the deal: Once you discover the health test or product that suits your needs, click the company's link on our site, and when you make a purchase, we may receive a modest commission from them, at no extra expense to you. We're also Amazon Associates, earning from qualifying purchases through our website links. Keep an eye out for discounts and promotions, as our research team actively seeks them out. While we can't guarantee lower prices every time, we assure you they'll never be higher.
We uphold editorial integrity.
Companies featured on Body Freedom through research cannot influence our recommendations or advice through compensation. Our guidance is firmly rooted in countless hours of diligent research. Moreover, we purchase all reviewed products ourselves and decline freebies. Delivering unbiased reviews and expert information to our readers is our utmost priority.
Body Freedom is independent and reader-supported. We have the highest editorial standards. Learn More
Photo by Body Freedom Collaborative
Jacqueline Gapinski, Ph.D.
Medical Writer
Jacqueline Gapinski, Associate Professor and Program Chair, specializes in Molecular Biosciences. With a Ph.D. from Johns Hopkins, she focuses on innovative teaching in genetics and molecular biology while mentoring students in research. She enjoys baking and outdoor activities with her children.
In an era demanding greater control and fewer compromises in reproductive health, the clamor for effective, non-hormonal birth control has reached a fever pitch. Years of navigating the side effects and systemic impacts of hormonal methods have left many searching for alternatives that work with the body, not against it. Enter Natural Cycles, a name synonymous with the digital evolution of fertility awareness. More than just a period tracker, it stands as the first app of its kind cleared by the FDA in the US and CE marked in Europe specifically as a method of contraception.1
But does this blend of technology and biology live up to its promise? Can an algorithm analyzing your morning temperature truly prevent pregnancy effectively and fit seamlessly into modern life? The digital sphere is rife with opinions, but reliable, in-depth analysis is harder to find.
That’s where we come in. Our dedicated team—comprising health journalists, a board-certified OB/GYN, and a panel of real-world testers—invested over six months and hundreds of hours rigorously evaluating Natural Cycles. We dissected the science, tracked daily usage, analyzed effectiveness data against clinical benchmarks, and gathered unfiltered feedback. This isn’t just another overview; it’s the comprehensive, no-nonsense deep dive you need to decide if Natural Cycles is the right choice for you.
What is Natural Cycles, Exactly? The Tech Behind the Tracking
At its core, Natural Cycles is a sophisticated system combining a highly sensitive basal thermometer (measuring temperature to two decimal places) with a proprietary algorithm housed within a smartphone app. Its fundamental goal: to pinpoint your fertile window with remarkable precision.
Unlike simple period trackers that rely on calendar calculations, Natural Cycles uses your unique physiological data.2 Every morning, before getting out of bed, you measure your oral temperature. This data, along with your period information (and optionally, results from Luteinizing Hormone tests), is fed into the app. The algorithm then analyzes these inputs against established physiological patterns to determine if you are likely fertile (“Red Day”) or not (“Green Day”).
Natural Cycles App
Key Features & Status:
Methodology: Digital interpretation of the Fertility Awareness Method (FAM), specifically temperature and cycle length data (enhanced by optional LH data).
FDA Cleared & CE Marked: Recognized by regulatory bodies as a contraceptive device when used as intended.
The Science Deconstructed: How Natural Cycles Predicts Fertility
Understanding Natural Cycles requires grasping the elegant hormonal shifts governing the menstrual cycle:
1
Basal Body Temperature (BBT)
Your body’s lowest resting temperature. After ovulation, the release of the hormone progesterone causes a slight but sustained increase in BBT (typically 0.2-0.5°C or 0.4-0.9°F). Natural Cycles detects this shift to confirm ovulation has occurred.
2
Luteinizing Hormone (LH)
This hormone surges approximately 24-36 hours before ovulation, triggering egg release. Optional LH tests (urine strips compatible with the app) can help the algorithm pinpoint the fertile window more precisely, especially during the initial learning phase or if temperature readings are ambiguous.
3
The Algorithm
This is the “brain” of the system. It doesn’t just look at one day’s temperature; it analyzes patterns over time, learns your unique cycle characteristics, and incorporates statistical modeling to predict the fertile window (typically around 6 days per cycle). It’s designed to err on the side of caution, often assigning more Red Days initially until it gains confidence in your cycle data.
Mechanism Breakdown:
Input
Physiological Indicator
How Natural Cycles Uses It
Basal Body Temp (BBT)
Post-ovulation progesterone increase
Confirms ovulation has occurred (retrospective)
Period Data
Start/end of menstrual cycle
Establishes cycle length & historical patterns
LH Test (Optional)
Pre-ovulation LH surge
Helps predict ovulation timing (prospective)
Algorithm Analysis
Combines all data + statistical modeling
Output: Daily Red (Fertile) / Green (Infertile) Status
To provide insights grounded in reality, we implemented a comprehensive 6-month testing protocol:
Diverse Tester Panel (n=12): Included women aged 25-40 with varying cycle regularity (within normal limits), previous birth control experiences (hormonal, barrier, none), and tech-savviness levels.
Metrics Tracked:
Adherence: Consistency of daily temperature measurement.
Usability: Ease of thermometer use (Bluetooth sync vs. manual), app navigation, clarity of information.
Algorithm Performance: Correlation of Red/Green days with expected fertile window (cross-referenced with secondary FAM indicators where possible), handling of data fluctuations (illness, poor sleep, travel).
Expert Oversight: Our reviewing OB/GYN provided clinical context and reviewed tester logs for any concerning patterns or misunderstandings of the method.
This approach allowed us to simulate the learning curve, daily commitment, and real-world variables that impact typical use effectiveness.
Effectiveness Under the Microscope: 93% vs. 98% – What It Really Means3
Natural Cycles often quotes two effectiveness rates, and understanding the difference is crucial:
Perfect Use (98% effective): This rate reflects usage exactly as directed – measuring temperature correctly every day, correctly identifying Red/Green days, and using protection (like condoms) or abstaining on all Red Days. This means 2 out of 100 women using it perfectly for a year might become pregnant.
Typical Use (93% effective): This rate reflects real-world usage, accounting for occasional missed measurements, incorrect interpretation, inconsistent use of protection on Red Days, or other human errors. This means 7 out of 100 women using it typically for a year might become pregnant.
Putting Effectiveness in Context:
Method
Typical Use Effectiveness
Perfect Use Effectiveness
Key Factor
Natural Cycles
93%
98%
User Adherence
Combined Pill
93%
>99%
Daily Adherence
Hormonal IUD (Mirena)
>99%
>99%
Device Placement
Copper IUD (Paragard)
>99%
>99%
Device Placement
Male Condom
87%
98%
Correct/Consistent Use
Traditional FAM
76-88% (varies widely)
95->99% (method dependent)
User Skill/Training
(Source: CDC, Natural Cycles Clinical Data)
Key Takeaway: Natural Cycles can be highly effective, approaching the perfect use rate of condoms or even the Pill, but this relies heavily on meticulous and consistent user behavior. The 5% gap between perfect and typical use underscores the importance of commitment.
Expert Insight: “The effectiveness of Natural Cycles hinges entirely on the user’s discipline and understanding.4 It’s not a passive method like an IUD. Patients must be counseled on the typical use rate and understand that ‘green means go’ only if they’ve used the method perfectly. We also stress it offers zero STI protection.” – Dr. Dina M. Gordon, MD
The Real-World User Experience: Our 6-Month Tester Journey
Our testers’ experiences painted a nuanced picture of life with Natural Cycles:
Getting Started: Onboarding was generally smooth. The app guides users through setup, tutorials, and the initial learning phase (often more Red Days). Testers appreciated the included high-quality basal thermometer, especially models with Bluetooth sync which minimized data entry errors.
The Daily Routine: Measuring temperature upon waking became second nature for most within a week or two. “It’s literally the first thing I do before even sitting up,” noted one tester. However, consistency was key. Sleeping in significantly or taking temp after getting up could skew results.
Interpreting Days: Green days provided peace of mind for many. Red days required conscious decision-making. “Having clear Red/Green days simplified things, but Red Days meant planning – either abstinence or ensuring we had condoms ready,” shared a tester in a long-term relationship.
App Usability: The interface was generally found to be clean and intuitive. Visual charts helped testers understand their cycle patterns over time. Some wished for more customization in data tracking beyond the core metrics.
Challenges & Solutions:
Illness/Fever: Fevers render temperature data unusable for fertility prediction. The app allows logging illness, which the algorithm considers. Testers learned to rely on barrier methods during and immediately after sickness.
Travel & Time Zones: Significant sleep disruption could impact BBT. Testers traveling across time zones found it took a few days for readings to normalize.
Alcohol: Heavy drinking could sometimes affect morning BBT. The app allows users to exclude questionable readings.
Motivation Dip: The daily commitment occasionally felt tedious for some, especially on weekends or holidays.
Tester Takeaway: “The biggest hurdle is consistency. If you travel frequently for work or have very erratic sleep, maintaining accurate readings can be challenging. But when you’re in a routine, it feels incredibly empowering to understand your body.” – Tester B, Age 31
PRO TIP #1: Set your alarm for the same time every single day, even on weekends, at least for the first few cycles, to take your temperature. Consistency is paramount for accurate readings.
PRO TIP #2: Use the ‘Exclude Temperature’ feature judiciously if you know a reading is off due to illness, significant alcohol intake, or major sleep disruption. Don’t guess – excluding is better than feeding the algorithm bad data.
PRO TIP #3: Consider using LH tests, especially in the first 1-3 cycles or if your cycles are slightly irregular. They provide valuable prospective information that complements the retrospective BBT data.
Pros and Cons: A Balanced Perspective
Pros
Completely Non-Hormonal: No hormonal side effects.
Increases Body Literacy: Users learn about their cycle patterns.
Effective (with Perfect Use): 98% efficacy rivals other methods.
FDA Cleared & CE Marked: Regulatory validation as contraception.
Discreet: App-based, no physical device worn continuously.
Potential Health Insights: Can help flag cycle irregularities.
Cons
Requires Daily Commitment: Measuring temp at the same time daily.
Value Perspective: While there’s an ongoing cost, it’s often comparable to or less than the monthly co-pay for hormonal birth control for some individuals, without the potential costs associated with managing side effects. Compared to the upfront cost of an IUD5 (which can be several hundred to over a thousand dollars without insurance), the annual fee is lower, but accumulates over time.
Is Natural Cycles Right For You? (And Who Should Avoid It)
This method isn’t a universal fit. Consider these profiles:
Natural Cycles is Likely a Good Fit If You:
Are highly motivated to use a non-hormonal method.
Are disciplined and can commit to a consistent daily routine (morning temperature).
Have relatively regular menstrual cycles (typically 21-35 days).
Are comfortable using technology (thermometer and app).
Are seeking to increase your body awareness and understand your cycle.
Are in a relationship where your partner is supportive and understands the method (cooperation on Red Days).
Are willing to abstain or consistently use barrier methods (like condoms) on Red Days.
Understand the difference between typical and perfect use effectiveness and accept the typical use rate.
You Might Want to Reconsider Natural Cycles If You:
Have very irregular periods or diagnosed conditions like PCOS that significantly disrupt cycles (consult a doctor first).
Have a lifestyle with highly inconsistent sleep patterns (e.g., shift work, frequent overnight travel).
Struggle with maintaining daily routines or find daily tracking burdensome.
Need protection against Sexually Transmitted Infections (STIs).
Are unwilling or unable to reliably abstain or use barrier methods during fertile periods.
Require a method with the absolute highest typical use effectiveness (like IUDs or implants).
Have medical conditions that cause persistent fluctuations in body temperature.
Natural Cycles vs. The Alternatives: Finding Your Place
vs. Traditional FAM: NC automates the interpretation and removes manual charting, potentially reducing user error in analysis, but still requires perfect data collection. Traditional methods might involve more indicators (like cervical mucus) offering cross-checks.
vs. Other FAM Apps: NC’s key differentiator is its specific FDA clearance as contraception.6 Many other apps are marketed for cycle tracking or achieving pregnancy, lacking the same regulatory validation and specific contraceptive effectiveness studies.
vs. Hormonal Methods (Pill, Patch, Ring, Implant, Hormonal IUD): NC avoids hormones but demands daily user action. Hormonal methods offer higher typical-use effectiveness and require less daily input but come with potential side effects.
vs. Barrier Methods (Condoms, Diaphragm): Barriers offer STI protection, which NC does not. Condom typical use effectiveness is lower than NC’s perfect use but higher than some traditional FAM typical use rates. NC requires action only on Red Days; condoms require action every time.
vs. Copper IUD: Offers highly effective, long-lasting, hormone-free protection with no user action required after insertion, but can sometimes increase menstrual bleeding or cramping.
The Final Verdict: Our Authoritative Recommendation
Natural Cycles represents a significant advancement in accessible, non-hormonal contraception. Its FDA clearance provides a level of validation many other digital FAM tools lack. Our testing and analysis confirm it can be a highly effective method (98% perfect use) for the right individual – one who is informed, motivated, and meticulously consistent.
However, the 93% typical use rate cannot be ignored. It highlights that real-world application requires unwavering discipline. Factors like illness, travel, inconsistent sleep, or simply forgetting to measure can widen the gap between perfect and actual protection. It demands active participation, not passive reliance.
Overall Rating: 4.3 / 5.0 Stars
We Recommend Natural Cycles For: Individuals seeking a non-hormonal, scientifically-backed method who understand and accept the commitment required for optimal effectiveness, prioritize body awareness, and have a lifestyle conducive to consistent daily tracking.
It’s Not For: Those needing the highest possible “set it and forget it” effectiveness, individuals with highly unpredictable cycles or lifestyles, or those unwilling/unable to manage Red Day protocols diligently.
Natural Cycles empowers users with profound insights into their own bodies.7 Used correctly, it’s a powerful tool for preventing pregnancy naturally. But success lies squarely in the user’s hands – a responsibility that must be embraced fully for the method to deliver on its promise.
Where to Buy & Special Offers
To ensure you receive the genuine product, correct thermometer, and access to customer support, we strongly recommend subscribing directly through the official Natural Cycles website.
Current Offer: New annual subscribers typically receive the basal thermometer included with their plan. Check the website for the latest bundles and promotions.
Avoid purchasing subscriptions or thermometers from unauthorized third-party resellers, as authenticity and support cannot be guaranteed.
How we reviewed this article:
Our experts vigilantly monitor the domain of health and wellness, promptly refreshing our articles with the latest discoveries. Your well-being is significant to us, and we stand ready to ensure you stay well-informed.
June 18, 2025
Current Version
June 18, 2025
June 18, 2025
Written By Jacqueline Gapinski, Ph.D. Edited By Suzanne Briggs Medically Reviewed By Robin M Voigt-Zuwala, PhD Copy Edited By Jun Xu
June 18, 2025
At Body Freedom, we rely solely on top-tier sources, such as peer-reviewed studies, to bolster the veracity of our content. Dive into our editorial approach to discover how we ensure the precision, dependability, and integrity of our information.
Pearson, J. T., Chelstowska, M., Rowland, S. P., Benhar, E., Kopp-Kallner, H., Scherwitzl, E. B., Acuna, J., Gemzell Danielsson, K., & Scherwitzl, R. (2021). Contraceptive effectiveness of an FDA-cleared birth control app: Results from the Natural Cycles U.S. cohort. Journal of Women’s Health, 30(6). https://doi.org/10.1089/jwh.2020.8547 ↩︎
Lundberg, O., Berglund Scherwitzl, E., Gemzell Danielsson, K., & Scherwitzl, R. (2018). Fertility awareness-based mobile application. The European Journal of Contraception & Reproductive Health Care, 23(2), 166–168. https://doi.org/10.1080/13625187.2018.1428298 ↩︎
Pearson, J. T., Chelstowska, M., Rowland, S. P., Mcilwaine, E., Benhar, E., Berglund Scherwitzl, E., … Scherwitzl, R. (2021). Natural Cycles app: contraceptive outcomes and demographic analysis of UK users. The European Journal of Contraception & Reproductive Health Care, 26(2), 105–110. https://doi.org/10.1080/13625187.2020.1867844 ↩︎
Rowland, S., Kallner, H. K., Gemzell-Danielsson, K., Trussell, J., Scherwitzl, E. B., & Scherwitzl, R. (2019). Impact of Sleep Habit on the Contraceptive Effectiveness of a Fertility Awareness-Based App [1O]. Obstetrics & Gynecology, 133, S162-S223. ↩︎
Benhar, E., van Lamsweerde, A., Krauss, K., Berglund Scherwitzl, E., & Scherwitzl, R. (2024). Contraceptive outcomes of the Natural Cycles birth control app: A study of Canadian women. medRxiv. https://doi.org/10.1101/2024.09.13.24313618 ↩︎
Berglund Scherwitzl, E., Lundberg, O., Kopp Kallner, H., Gemzell Danielsson, K., Trussell, J., & Scherwitzl, R. (2017). Perfect-use and typical-use Pearl Index of a contraceptive mobile app. Contraception, 96(6), 420-425. https://doi.org/10.1016/j.contraception.2017.08.014 ↩︎
Grenfell, P., Tilouche, N., Shawe, J., & French, R. S. (2020). Fertility and digital technology: Narratives of using smartphone app ‘Natural Cycles’ while trying to conceive. Sociology of Health & Illness, 43(1), 24-39. https://doi.org/10.1111/1467-9566.13199 ↩︎
