Natural Cycles works as a contraceptive, but how well it works depends heavily on how consistently you use it and what you’re switching from. With typical use, about 5 to 7 out of 100 women using the app will become pregnant within a year. With perfect use, that number drops to around 1 to 2. Whether that level of protection is “worth it” comes down to your tolerance for risk, your willingness to follow the daily routine, and what you’d be replacing.
How Effective It Actually Is
The most cited study on Natural Cycles, published in BMJ Open, followed over 16,000 women and found a typical use failure rate of about 6.1 pregnancies per 100 woman-years. Perfect use, meaning you take your temperature every morning and either abstain or use protection on every red (fertile) day, brought the rate down to 1.0. A more recent study of nearly 8,800 Canadian women found slightly better typical use numbers: a 4.3 failure rate, with perfect use at 1.7.
For context, the typical use failure rate of the pill is about 7 per 100 women per year, mostly because people forget doses or refill prescriptions late. Male condoms sit around 13 with typical use. IUDs and implants are under 1. So Natural Cycles lands in roughly the same effectiveness range as the pill when used typically, but nowhere near a hormonal IUD or implant.
One surprising detail from the BMJ Open study: your previous contraceptive method predicts how well you’ll do with Natural Cycles. Women who previously used condoms had the lowest failure rate at 3.5, while women switching from the pill had the highest at 8.1. The researchers suggested this is because hormonal methods can temporarily disrupt cycle patterns after stopping, making the algorithm less accurate during the transition. Women who were already tracking their cycles or using barrier methods tended to adapt faster.
What Using It Looks Like Day to Day
Natural Cycles works by tracking your basal body temperature, the lowest temperature your body reaches during rest, to identify when you’re fertile. After ovulation, your body temperature rises slightly (about 0.2 to 0.5°C) and stays elevated until your next period. The app’s algorithm learns your personal cycle pattern over time and assigns each day a color: green for low fertility, red for high fertility when you need to abstain or use a condom.
The daily commitment is real. You need to measure your temperature first thing in the morning before getting out of bed, ideally at a consistent time. In the first few months, while the algorithm is still learning your cycle, you’ll see more red days, sometimes 10 to 15 per cycle. As it gathers data, the red window typically narrows. You can also log optional LH (ovulation) test results to help the app pinpoint your fertile window more precisely, though this isn’t required.
If you travel across time zones, have irregular sleep, drink alcohol the night before, or are fighting off an illness, your temperature reading may be unreliable. The app lets you flag these readings so it can exclude them, but frequent disruptions mean less data for the algorithm and potentially more red days as a safety buffer.
Compatible Devices
You don’t need to use a traditional oral thermometer. Natural Cycles integrates with wearable devices that measure temperature overnight, which removes the hassle of remembering to take your temperature the moment you wake up. Oura Ring (Gen 2, Gen 3, and Ring 4 with an active Oura membership) syncs temperature data automatically. You just wear it to bed, open the Oura app in the morning, and the data flows into Natural Cycles.
Apple Watch integration is also available through Apple Health, though Natural Cycles doesn’t specify which models are required. If you already own one of these devices, the daily routine becomes significantly easier since the temperature measurement happens passively while you sleep.
What It Costs
Natural Cycles offers monthly and annual subscription plans. The annual plan works out cheaper per month, as is typical with subscription pricing. Both tiers are FSA and HSA eligible, which means you can get reimbursed through your benefits account. You can’t pay directly with an FSA or HSA card on the Natural Cycles website, but you’ll receive an itemized receipt after purchase that you can submit for reimbursement.
Compared to hormonal birth control with insurance, Natural Cycles may cost more out of pocket. Compared to paying full price for the pill without insurance, or buying condoms every month, it’s competitive. If you already own an Oura Ring or Apple Watch, the only ongoing cost is the subscription itself. If you need to buy a basal thermometer separately, that’s a one-time purchase of roughly $10 to $20.
FDA Clearance and What It Means
Natural Cycles received FDA clearance in the U.S. as a Class II medical device, the same regulatory category as condoms and pregnancy tests. This means the FDA reviewed evidence that the app performs as intended, not that it endorses it as superior to other methods. The clearance covers both its use for preventing pregnancy and for planning pregnancy. It’s approved for women 18 and older.
Who Gets the Most Out of It
Natural Cycles tends to work best for women with relatively regular cycles who are disciplined about daily temperature measurement. If you’re in a stable relationship where an unplanned pregnancy would be unwelcome but not catastrophic, the risk profile may feel acceptable. Many users choose it specifically because they want to avoid hormones and their potential side effects, and for that group, it fills a gap that few other options cover with this level of data and structure.
It’s a harder sell if you have very irregular cycles, frequently disrupted sleep, or if an unplanned pregnancy would be a serious problem. The 5 to 7 percent typical use failure rate means that over several years of use, the cumulative odds of an unplanned pregnancy are meaningful. For someone who needs the highest possible protection, a long-acting method like an IUD remains significantly more reliable.
The women who report the highest satisfaction tend to be those who value understanding their cycle and are willing to treat the daily routine as a small but non-negotiable habit. If measuring your temperature every morning sounds tedious rather than empowering, the app will likely frustrate you before it helps you.