The Billings Ovulation Method
A fertility awareness based method that identifies the fertile window through standardized cervical mucus observations and sensation, without temperature charting or hormone monitors.
Source
WHO multicentre trial of the Billings Ovulation Method, 1981.
Full citation
World Health Organization. A prospective multicentre trial of the ovulation method of natural family planning. I. The teaching phase. Fertil Steril. 1981;36(2):152-158.
Fertility and Sterility, via PubMed. https://pubmed.ncbi.nlm.nih.gov/7021189/
How to read these numbers
Perfect use describes pregnancies per 100 women per year when the method is followed exactly as taught. Typical use describes pregnancies per 100 women per year across all users in a study, including cycles where the rules were not followed perfectly. Numbers come from specific published studies of specific populations and instruction settings; they are not guarantees for any individual. Methodology, sample size, and how a study defines a pregnancy or a cycle of use all affect the result, so figures from different methods are not always directly comparable.
This page is educational and is not medical advice. For decisions about contraception, fertility, or reproductive health, talk with a qualified clinician. See the medical disclaimer for details.
Before choosing a method
Before comparing method names, it helps to understand how NFP works, how method rules are learned, and how effectiveness claims should be read.
The Billings Ovulation Method is a mucus-only fertility awareness based method. Users observe the sensation at the vulva throughout the day and the appearance of any mucus, then record those observations using the method's standardized vocabulary. The method's rules then translate those observations into fertile and infertile days.
Billings was developed in Australia beginning in the 1950s and has been studied in several countries. A multinational trial coordinated by the World Health Organization examined whether the method could be taught across very different settings.
What this method is
Billings is a defined system, not just the general idea of paying attention to mucus. The vocabulary and rules are taught by instructors who use the same terms across countries. That shared language is part of what makes it a method rather than a personal practice.
What this method observes
The user pays attention to the sensation at the vulva (dry, moist, lubricative) and to any mucus that appears. The presence and quality of mucus changes across the cycle as estrogen and progesterone shift, and the method uses those changes, including the identification of a 'peak' day, to mark the boundaries of the fertile window.
How it generally works
Each day, the user records the day's sensation and mucus pattern using the method's standardized terms. The chart, read across the cycle, shows when fertile-type signs appear, when they peak, and when they close. Specific rules then define which days are considered infertile, fertile, or post-peak infertile.
Who it may fit
- People who prefer not to use devices, hormone tests, or temperature thermometers.
- People comfortable with consistent daily observation.
- People who have access to a trained Billings teacher.
Who may need extra support
- People in postpartum, breastfeeding, or perimenopause, where mucus patterns can be harder to read.
- People with conditions that affect cervical fluid.
- People who would prefer a more objective hormonal signal in addition to mucus, who may be better served by a hormone-monitor based approach.
What this method does not guarantee
Like every fertility awareness based method, Billings does not guarantee that pregnancy will not occur. Effectiveness depends on instruction, consistent daily observation, and following the rules. The method describes what is observed; it does not diagnose medical conditions.
Instruction and learning considerations
Billings is normally taught one-on-one. Instructors use the same vocabulary and the same chart format, which is why two users in different countries can describe the same observation in the same words. Self-teaching from a book or video is possible but is not equivalent to the conditions described in the published research.
Misconceptions worth clearing up
- Billings is not the rhythm method; it does not use cycle counting to predict the fertile window.
- It is not 'just checking mucus' in a casual sense; it uses defined observations and rules.
- It is not an app and does not depend on prediction algorithms.
- Mucus observation is a learnable skill, not a special talent.
Related research and reading
- WHO Billings trial, /research/who-billings-trial
- Cervical mucus, /glossary/cervical-mucus
- Fertile window, /glossary/fertile-window
- Ovulation, /glossary/ovulation
- Is NFP the rhythm method, /questions/is-nfp-the-rhythm-method
- How effective is NFP, /questions/how-effective-is-nfp
- Do I need a certified instructor, /questions/do-i-need-a-certified-instructor
- The science behind NFP, /science
- Browse all methods, /methods
Perfect-use checklist
What perfect use of the Billings method assumes.
The published perfect-use number for this method describes couples who behaved a specific way during a specific study. This list summarises those behaviors so the number is read in context.
Source context. Behaviors assumed in the WHO multicentre Billings trial, 1981, and in subsequent Billings effectiveness research.
- Taught one-on-one by a trained Billings teacher, using the standardized vocabulary on the chart.
- Observe both vulvar sensation (dry, moist, lubricative) and any visible mucus across the day, not just at one moment.
- Record the day's observation on the chart by evening, every day of the cycle.
- Identify the Peak Day according to the method's definition, not by guess.
- Treat any day with fertile-type sensation or mucus as fertile, including ambiguous days.
- On days the rules mark fertile, abstain as the couple has agreed in advance.
- Use the post-Peak rules exactly as taught to mark the close of the fertile window.
- Use the stage-specific Billings protocol during postpartum, breastfeeding, or perimenopause cycles.
The published trial measured couples who completed structured teaching with a trained Billings instructor. Self-taught practice is not what those numbers describe.
Educational summary, not individualized medical advice. For decisions about your body or your cycle, talk with a clinician or a certified instructor. See the medical disclaimer.
Reading the checklist
How to interpret perfect use.
What does perfect use actually mean?
Perfect use is a research category, not a personality test. It describes cycles where the couple followed every rule of the method exactly as taught for the entire study period. Researchers count a cycle as perfect use only when the charting, the timing, and the abstinence or barrier choices all matched the protocol. Anything else gets counted under typical use.
Why do real-world results often differ from perfect use?
Daily life adds variables a study cannot control. People travel, get sick, sleep poorly, miss an observation, or interpret a borderline sign in their own way. A couple may also choose to use a fertile day knowing the risk. None of that is failure of the method itself; it is the gap between an ideal protocol and lived behavior, which is exactly what the typical-use number captures.
Is perfect use realistic for most couples?
Many couples reach perfect use for stretches of time, especially after working with a certified instructor and settling into a routine. Sustaining it across years, life stages, and unusual cycles is harder. The honest read is that perfect use shows what the method can do when followed exactly, and typical use shows what tends to happen across a broad population.
How should I use this checklist?
Treat it as context for the published number, not as a personal grading rubric. If most items match how you plan to learn and chart, the perfect-use figure is a reasonable upper bound for your situation. If several items do not match, the typical-use figure is closer to what to expect. For decisions specific to your body, talk with a clinician or a certified instructor.
Sources referenced
- [1]
World Health Organization. A prospective multicentre trial of the ovulation method of natural family planning. I. The teaching phase. Fertil Steril. 1981;36(2):152-158.
Fertility and Sterility, via PubMed ↗ - [2]
Billings Ovulation Method, public information page.
Billings Ovulation Method Association ↗
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Effectiveness FAQ
How effective is the Billings method?
Quick answers using the numbers from this method's primary published study, with links to the full comparison.
See the full effectiveness comparisonHow effective is the Billings method?
Published studies report 97% perfect-use effectiveness and 78 to 88% typical-use effectiveness for Billings at one year. Source: WHO multicentre trial of the Billings Ovulation Method, 1981.
What is the perfect-use effectiveness of Billings?
97%. Perfect use means the method's rules were followed on every applicable day, as defined in the published study.
What is the typical-use effectiveness of Billings?
78 to 88%. Typical use includes everyone in the study, including users who skipped observations or had intercourse during the fertile window.
Is Billings as effective as hormonal birth control?
On perfect use, Billings reports 97%, which is in the same range as hormonal methods such as the pill (about 99 percent perfect use). Typical-use numbers depend on the population, instruction, and how the study defined unintended pregnancy.