Charting your cycle can prevent or plan pregnancy, and the method makes the difference

Key takeaways

• Nearly all pregnancies trace to sex during a six-day window that ends on the day of ovulation, a landmark 1995 study found, and the odds rise as ovulation nears¹.
• In widely used tables, typical use of fertility awareness methods as a group leads to about 24 pregnancies per 100 women a year, though well-taught methods that combine signs have done far better in some studies⁴⁶⁷.
• In August 2018, the FDA authorized Natural Cycles as the first app marketed for birth control, with a 6.5% typical-use failure rate in studies of 15,570 women⁸.
• To conceive, the American Society for Reproductive Medicine says sex every one to two days during the fertile window works best³.
• In 2025, Arkansas began requiring insurers to cover “restorative reproductive medicine,” an approach the leading U.S. group of OB-GYNs calls unproven¹⁰¹¹.

In one study, couples had more sex during a woman’s most fertile days, even though they weren’t trying for a baby.

The 2004 study followed 68 women who used an IUD or had their tubes tied². Sex was 24% more frequent during the six fertile days of the cycle than on other days without bleeding². The authors suggested biology may nudge the timing, and they warned that occasional unprotected sex may carry more risk than chance alone would predict².

That six-day window is the heart of fertility awareness. You learn which days can lead to pregnancy, then avoid sex or use a barrier on those days, or aim for them if you want a baby. Methods range from counting days to charting temperature and mucus. In 2018, the Food and Drug Administration (FDA) authorized the first birth control app⁸.

People choose these methods for many reasons: religious faith, a wish to avoid hormones or devices, side effects from other methods, or a desire to understand their own bodies. All of those are valid. Below, we cover how well each method works, how the same skills help with conception, and what’s behind the debate over “restorative reproductive medicine.”

Six days a cycle can lead to pregnancy

The key study came in 1995. Researchers followed 221 healthy women who were trying to conceive. The women saved urine samples every day and recorded each time they had sex¹.

Hormone traces in the urine let researchers estimate the day each woman ovulated, or released an egg. Across 625 cycles, 192 pregnancies began¹.

Conception happened only when couples had sex during a six-day span ending on the estimated day of ovulation¹. The chance of pregnancy rose from about 10% for sex five days before ovulation to about 33% for sex on ovulation day¹. The study also found that timing sex around ovulation didn’t affect whether the baby was a boy or a girl¹.

The American Society for Reproductive Medicine (ASRM), a group for fertility doctors, still uses that six-day window³. The hard part is that ovulation can shift from cycle to cycle. Fertility awareness is a set of ways to find that moving target.

Four ways to find your fertile days

Counting days. Calendar methods predict fertile days from past cycle lengths. The Standard Days Method treats days 8 through 19 of every cycle as fertile and is meant for people whose cycles are usually 26 to 32 days long⁴. Older calendar rhythm methods use a formula based on at least six months of recorded cycles⁴.

Checking cervical mucus. As ovulation nears, secretions from the cervix increase and turn clear, slippery and stretchy³⁴. The Billings, or ovulation, method treats days as fertile from when secretions start until a few days after the “peak day,” the last day of clear, slippery secretions⁴. The simpler TwoDay Method asks one question: did you notice secretions today or yesterday?⁴ The Creighton Model codes mucus in a standard way and is the charting system behind a medical approach called NaProTechnology⁹.

Taking your temperature. After ovulation, resting body temperature rises by about 0.2 to 0.5 degrees Celsius, or 0.4 to 1.0 degrees Fahrenheit⁴. Because the rise comes after ovulation, it confirms that the fertile time has passed. The rules call for three full days of higher readings before unprotected sex⁴.

Combining signs or measuring hormones. Symptothermal methods use both mucus and temperature, and one version, Sensiplan, adds a double-check rule⁴⁹. Hormone monitors, such as the Marquette method’s device, read hormone levels in urine⁹. Drugstore ovulation kits detect the surge of luteinizing hormone (LH) that comes just before ovulation³.

In 2015 guidance, Britain’s Faculty of Sexual and Reproductive Healthcare (FSRH) advised against relying on any single sign to avoid pregnancy. Combining signs works better, and learning from a trained teacher helps⁵.

Perfect use and typical use are very different numbers

Two numbers describe any birth control method. “Perfect use” means following the rules every time. “Typical use” counts real life, including mistakes and skipped rules⁶.

For fertility awareness, the gap is wide. In researcher James Trussell’s widely used tables, typical use of these methods as a group led to 24 pregnancies per 100 women in the first year⁶. With no method at all, about 85 of 100 women get pregnant in a year⁶. By our math, fertility awareness as typically used prevents about 61 of every 85 pregnancies that would otherwise happen.

For comparison, Trussell’s tables list typical-use rates of 18 per 100 for male condoms and 9 per 100 for the pill⁶. With perfect use, the Standard Days, TwoDay and ovulation methods ranged from 3 to 5 per 100⁶.

The best results come from well-taught methods that combine signs. WHO’s handbook lists 2 pregnancies per 100 women in a year of typical symptothermal use⁴. A 2018 review was led by Rachel Peragallo Urrutia of the University of North Carolina. It found the lowest typical-use rates for Sensiplan and the Marquette monitor, between 1.8 and 6.8 per 100 new users⁷.

But that same review is a reason for caution. It looked at 53 studies of 14 methods and rated none of them high quality⁷. Typical-use estimates for most methods ran from 10 to 33 pregnancies per 100 women a year⁷.

Why do studies disagree so much? Trussell pointed to several reasons⁶:

• Study groups differ in age, fertility and how often they have sex.
• Most attempts to separate “method” failures from “user” failures were done incorrectly.
• Women who drop out of studies may get pregnant more often than those who stay.
• Perfect-use figures often rest on just one or two studies.

Fertility awareness methods compared

Figures are pregnancies per 100 women in the first year of typical use.

Method	What you track	Typical-use pregnancies per 100 women a year	Effort	Best for
Standard Days	Cycle days 8 to 19	124	Low	Regular cycles of 26 to 32 days
Calendar rhythm	Past cycle lengths and a formula	No reliable figure4	Low to medium	Very regular cycles, as a backup to other signs
TwoDay	Secretions today or yesterday	144	Low	People who want a simple daily check
Ovulation (Billings)	Mucus pattern and peak day	234	Medium	Couples willing to learn mucus signs from a teacher
Creighton Model	Mucus with standardized codes	No standard typical-use figure9	Medium to high	Charting that a trained clinician can also review
Temperature only	Waking temperature	No reliable figure4	Medium	Confirming ovulation, mostly with other signs
Symptothermal (such as Sensiplan)	Mucus plus temperature	2 in WHO’s handbook; as low as 1.8 for Sensiplan479	High	Committed couples who learn the rules well
Hormone monitor (Marquette)	Urine hormones, often with mucus	6.7 to 14 across studies9	Medium, plus a daily urine test	People who prefer a device reading
Natural Cycles app	Waking temperature plus cycle data	6.58	Medium, plus a basal thermometer	Adults 18 and older who will measure daily

One app is FDA-authorized as birth control, but most aren’t

In August 2018, the FDA allowed Natural Cycles to be marketed as the first mobile app for preventing pregnancy⁸. Users take their temperature each morning with a sensitive basal thermometer and enter it with their cycle data. An algorithm then flags fertile days, when users should abstain or use a condom⁸.

The FDA based its decision on studies of 15,570 women who used the app for an average of eight months⁸. The perfect-use failure rate was 1.8%, which the FDA explained as 1.8 pregnancies per 100 women using the app for a year. The typical-use failure rate was 6.5%⁸. The FDA release didn’t say who ran or paid for those studies, so read them as data from one product’s own users.

The app is meant for premenopausal women 18 and older, not for those whose health would be at serious risk in pregnancy⁸. The FDA’s decision created a new device category, so later apps with the same purpose can seek clearance by showing they match it⁸.

That authorization doesn’t extend to the many period and fertility apps that predict your fertile days. The 2018 UNC-led review warned that many apps and devices marketed this way haven’t been tested well⁷. And in one study cited by ASRM, calendar-based predictions found the actual day of ovulation at most 21% of the time³.

Fertility apps also collect very personal data. Our article on locking down health apps covers privacy, and a later article in this series looks at cycle-tracking apps in detail.

The same skills can help you get pregnant

Fertility awareness isn’t only for avoiding pregnancy. ASRM’s 2022 committee opinion on natural fertility puts it to work for conception³:

• Aim for the fertile window. Sex every one to two days during the window works best, and ASRM says couples shouldn’t be told to limit how often they have sex.
• Watch for slippery mucus. Pregnancy rates peaked at about 38% on the day of peak mucus.
• Consider urine LH kits. In a randomized trial, they shortened the time to pregnancy. Ovulation can follow the surge by up to two days, and false positives occur in about 7% of cycles.
• Skip the rituals. No evidence shows that sexual position or lying still afterward helps. Our article on fertility myths covers lubricants and other common worries.

Charting for a baby can turn into a monthly test that feels like pass or fail. If trying to conceive ever leaves you unable to cope, or thinking about suicide, you can call or text 988, the Suicide and Crisis Lifeline, at any hour¹⁵.

Restorative reproductive medicine: what it is and why it’s debated

Restorative reproductive medicine, or RRM, looks for and treats the causes of infertility. Its tools include cycle charts, hormone tests, ultrasound and sometimes surgery¹⁰¹¹. Arkansas’s 2025 law describes RRM as an approach that tries to work with, or restore, the body’s normal reproductive function¹¹. The law names the Billings and Creighton methods¹¹.

Supporters see charting as both family planning and a diagnostic tool. RRM Academy, an education nonprofit that promotes the approach, says a trained clinician can read a chart for signs of ovulation problems or a short second half of the cycle⁹. It cites no data on how accurate those readings are.

The Arkansas sponsor, Rep. Alyssa Brown, said RRM costs less than IVF and added, “This doesn’t limit anyone’s ability to access IVF”¹¹.

Critics see it differently. The American College of Obstetricians and Gynecologists (ACOG) has called RRM an “unproven concept,” The 19th reported¹⁰. ACOG warned it can delay pregnancy, lead to unneeded surgery and put the burden on women, though male infertility is just as common¹⁰.

ASRM, many of whose members provide IVF, has described RRM as more ideology than medicine¹⁰¹¹. The patient group Resolve warned that framing RRM as a first step before IVF could take choices away from patients¹¹. News coverage of the debate cited no success-rate data, and the Arkansas sponsor’s claim of higher success rates came without published figures¹⁰¹¹.

How policy has moved, by date:

• February 2025: An executive order directed federal officials to recommend ways to protect IVF access and lower its costs¹².
• April 2025: Arkansas passed the first state RRM law, Act 859, effective in August. Insurers, including the state’s Medicaid expansion, must cover RRM. Programs funded by Title X, the federal family planning program, must use fertility awareness methods¹⁰¹¹¹².
• 2025: The Louisiana House passed a resolution asking the state medical board and health department to study RRM resources and report back¹². A federal bill called the RESTORE Act, which failed in 2024, was introduced again in Congress¹⁰.
• By October 2025: The administration announced that $1.5 million in Title X funds would go to fertility training centers¹³.
• October 2025: A White House announcement promised a lower price for a common fertility drug through TrumpRx and a new way for employers to offer fertility benefits¹².
• May 2026: The administration released an IVF insurance policy with draft coverage rules for public input. ASRM called it promising but short of the nationwide IVF coverage the president had promised¹⁴.
• By June 2026: The journal Fertility and Sterility had published a series examining RRM and other alternatives to IVF, ASRM reported¹⁴.

What the evidence says

Claim	What the research shows	Evidence level
Pregnancy comes from sex in a six-day window ending at ovulation	1995 study of 221 women and 625 cycles; used in ASRM guidance13	Strong evidence
Sex every one to two days in the window helps conception	ASRM committee opinion3	Strong evidence
Well-taught symptom-based methods prevent pregnancy reliably	Low rates in some studies, but none of 53 studies rated high quality47	Promising but early
Natural Cycles works as authorized	6.5% typical-use failure in 15,570 women; large, but drawn from one product’s own users8	Promising but early
Urine LH kits help time sex	One randomized trial shortened time to pregnancy3	Promising but early
Calendar apps can pinpoint ovulation	At most 21% accuracy in one study3	Evidence says no, or unsafe
Timing sex can choose a baby’s sex	Timing made no practical difference to a baby’s sex1	Evidence says no, or unsafe
RRM works better than standard fertility care	No success-rate data cited in coverage; ACOG calls it unproven1011	Not enough evidence

Choosing a method that fits your values

Fertility awareness rewards a habit many natural-health readers already have: paying close attention to the body. A chart kept over months can show patterns no single doctor visit would catch, and it belongs to you.

It also asks for teamwork. On fertile days, both partners must agree to abstain or use a barrier, and typical-use numbers show how often real life gets in the way⁶. Couples who chart for faith or conviction may accept that trade-off knowingly. That’s a legitimate choice.

If avoiding pregnancy is critical for your health, the FSRH says fertility signs shouldn’t be your only method⁵. A clinician or trained teacher can help you weigh options without pressure⁵.

Questions readers ask

The bottom line

Fertility awareness is a family of methods, not one. Well-taught methods that combine mucus and temperature have done far better than counting days alone, though the research is thin. Your results depend on the method, the teaching and how closely you both follow the rules.

The same knowledge helps couples who want a baby: regular sex in the fertile window beats rituals. RRM has gained political support, but its claims still need trials. Whatever your reasons for charting, choose with clear numbers in hand.

Keep exploring: endometriosis diagnosis without surgery.

Related reading

• Endometriosis can often be diagnosed without surgery now, so treatment can start sooner
• Health apps share more than you think, and you can lock yours down
• What protects your data when HIPAA doesn’t cover most health apps
• Your wearable’s best number is your own normal, not the average
• Faith shapes how people eat, fast and decide, and your clinician should know

Sources

1. Wilcox AJ, Weinberg CR, Baird DD. “Timing of sexual intercourse in relation to ovulation: effects on the probability of conception, survival of the pregnancy, and sex of the baby.” New England Journal of Medicine, 1995;333(23):1517–1521 (abstract via CARTA bibliography). carta.anthropogeny.org
2. Wilcox AJ, et al. “On the frequency of intercourse around ovulation: evidence for biological influences.” Human Reproduction, 2004;19(7):1539–1543 (CDC Stacks copy). stacks.cdc.gov
3. Practice Committees of the American Society for Reproductive Medicine and the Society for Reproductive Endocrinology and Infertility. “Optimizing natural fertility: a committee opinion.” Fertility and Sterility, 2022;117(1):53–63. integration.asrm.org
4. World Health Organization and Johns Hopkins Center for Communication Programs. “Fertility Awareness Methods,” Chapter 18 in Family Planning: A Global Handbook for Providers (online edition). fphandbook.org
5. Faculty of Sexual & Reproductive Healthcare, Clinical Effectiveness Unit. “Fertility Awareness Methods.” FSRH, June 2015 (updated November 2015). cosrh.org
6. Trussell J. “Contraceptive Efficacy.” Global Library of Women’s Medicine, 2014. glowm.com Efficacy/item/374
7. UNC Health. “Review of scientific evidence on effectiveness of fertility awareness-based methods for contraception underscores need for higher quality studies” (on Peragallo Urrutia R, et al., Obstetrics & Gynecology, 2018). UNC Health, August 9, 2018. news.unchealthcare.org
8. U.S. Food and Drug Administration. “FDA allows marketing of first direct-to-consumer app for contraceptive use to prevent pregnancy.” FDA news release, August 2018.
9. RRM Academy (pro-RRM education nonprofit). “Fertility awareness methods compared.” Published June 12, 2026; updated October 14, 2026. rrmacademy.org
10. Vollers AC. “As Republicans spar over IVF, some turn to ‘restorative reproductive medicine’.” The 19th, August 2025. 19thnews.org
11. Vrbin T. “Infertility experts warn against ‘restorative reproductive medicine,’ promoted by new Arkansas law.” Arkansas Advocate, June 30, 2025. arkansasadvocate.com
12. Barnauskas MK. “Fertility Care and IVF Access in 2025: State Legislation and Federal Policy Highlights.” MultiState, November 5, 2025. multistate.us
13. KFF. “Fertility Awareness-Based Methods to Prevent Pregnancy.” KFF, October 16, 2025 (modified January 8, 2026). kff.org
14. American Society for Reproductive Medicine. “June 2026: Advocacy in Action.” ASRM, June 2026. asrm.org
15. Substance Abuse and Mental Health Services Administration. “In Crisis” (988 Suicide & Crisis Lifeline). SAMHSA, updated June 3, 2026. samhsa.gov