Standard Days Method
A calendar-based fertility awareness method designed for people whose cycles consistently fall within a specific range of cycle lengths. It is simpler than biomarker-based methods, but it applies to a narrower set of users.
Perfect use
95%
Typical use
88%
Biomarkers
Cycle length
Organization
Developed at the Institute for Reproductive Health, Georgetown University
Official site ↗Source
Arevalo, Jennings, Sinai, Standard Days Method efficacy study, Contraception 2002.
Full citation
Arevalo M, Jennings V, Sinai I. Efficacy of a new method of family planning: the Standard Days Method. Contraception. 2002;65(5):333-338.
Contraception (Elsevier), via PubMed. https://pubmed.ncbi.nlm.nih.gov/12057784/
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 Standard Days Method is a calendar-based fertility awareness method developed at the Institute for Reproductive Health at Georgetown University. It is designed for people whose cycles are consistently within the range studied for the method. Users avoid intercourse on a defined set of cycle days when pregnancy is most likely, traditionally days 8 through 19, and the original CycleBeads tool was created to help track those days visually.
Standard Days is the simplest of the modern fertility awareness based methods, but that simplicity is also its main limitation: it relies on cycle length staying within the range it was designed for.
What this method is
The Standard Days Method assumes that, for users whose cycles consistently fall within the studied range, the highest-risk days for pregnancy can be approximated by counting from the first day of the period. The method then defines a fixed set of cycle days as fertile and asks couples to avoid intercourse on those days if they are trying not to conceive.
What this method observes
It observes one thing: cycle length. It does not use cervical mucus, basal body temperature, or hormone testing. The user notes when their period starts, counts the cycle days, and uses the method's defined fertile range.
How it generally works
On day one of menstruation, the user starts counting. From day 8 through day 19 of the cycle, intercourse is avoided if the goal is to prevent pregnancy. After day 19, intercourse is considered acceptable until the next period begins. Tools like CycleBeads make the count easier to follow.
Who it may fit
- People whose cycles consistently fall within the cycle-length range the method was designed for.
- People who want a simple, low-effort approach and do not want to track biomarkers.
- People who do not have access to instructor-led methods.
Who may need extra support
- People with cycles that often fall outside the studied range.
- People in the postpartum or breastfeeding stage.
- People in perimenopause.
- People with conditions like PCOS or other causes of cycle irregularity.
What this method does not guarantee
The Standard Days Method does not adapt to a cycle that turns out longer or shorter than usual. If ovulation happens earlier or later than the assumed range, the fixed fertile window will not match real biology in that cycle. Effectiveness in the published research describes users who met the cycle-length eligibility criteria; outside that group, the assumptions break down.
Instruction and learning considerations
Standard Days is straightforward to learn, which is part of its appeal in low-resource settings. That same simplicity, however, means the method does not give the user any new information when their body is not following the usual pattern. Combining a calendar method with biomarker observations is not what the published research evaluated.
Misconceptions worth clearing up
- Standard Days is not the same as the older rhythm method; it was designed and tested as a defined modern method.
- It is not, however, equivalent to biomarker-based methods, because it does not respond to changes in this cycle.
- Simplicity is not the same as safety. A method can be easy to use and still be a poor fit for an individual's biology.
- Avoiding cycle days 8 through 19 is not a generic rule for everyone; it only describes the Standard Days protocol for eligible users.
Related research and reading
- Is NFP the rhythm method, /questions/is-nfp-the-rhythm-method
- Can I use NFP with irregular cycles, /questions/can-i-use-nfp-with-irregular-cycles
- Rhythm method, /glossary/rhythm-method
- Fertile window, /glossary/fertile-window
- Ovulation, /glossary/ovulation
- The science behind NFP, /science
- Browse all methods, /methods
Perfect-use checklist
What perfect use of the Standard Days 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 Arevalo, Jennings, and Sinai, Standard Days Method efficacy study, Contraception 2002.
- Confirm cycle eligibility first: cycles consistently 26 to 32 days long, the range the study enrolled.
- Track every cycle. If a cycle falls outside the 26 to 32 day range, the method's assumptions no longer apply.
- Mark cycle day 1 on the day menstruation starts, with no skipped or estimated start dates.
- On cycle days 8 through 19, abstain from intercourse if the goal is to prevent pregnancy.
- Use a CycleBeads aid, an app, or a written chart consistently; do not switch tracking systems mid-cycle.
- If two cycles within a year fall outside the 26 to 32 day range, stop relying on Standard Days and choose a different method.
- Do not use Standard Days during postpartum, breastfeeding return, or perimenopause cycles, when length variability is expected.
Standard Days does not adapt to a single early or late ovulation. Its protections come from cycle-length eligibility, not from biomarker observation.
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]
Arevalo M, Jennings V, Sinai I. Efficacy of a new method of family planning: the Standard Days Method. Contraception. 2002;65(5):333-338.
Contraception (Elsevier), via PubMed ↗ - [2]
Standard Days Method overview.
Institute for Reproductive Health, Georgetown University ↗
Continue reading
Effectiveness FAQ
How effective is the Standard Days 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 Standard Days method?
Published studies report 95% perfect-use effectiveness and 88% typical-use effectiveness for Standard Days at one year. Source: Arevalo, Jennings, Sinai, Standard Days Method efficacy study, Contraception 2002.
What is the perfect-use effectiveness of Standard Days?
95%. 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 Standard Days?
88%. Typical use includes everyone in the study, including users who skipped observations or had intercourse during the fertile window.
Is Standard Days as effective as hormonal birth control?
On perfect use, Standard Days reports 95%, 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.