Science and Research
Lunarmates is built on a foundation of published research into hormonal cycles, behaviour, and relationships.
The content on Lunarmates is intended for informational and relationship purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Every person is different, and cycles vary widely. Always consult a qualified health professional for medical concerns related to menstrual health or reproductive wellbeing. Lunarmates should not be used as a method of contraception or to plan a pregnancy.
Lunarmates predicts the menstrual cycle from one simple input: the date the period starts. That's the only information we ask for.
From logged dates, we calculate average cycle length using up to six most recent cycles, so the estimate adapts naturally as patterns drift over time, rather than assuming everyone follows a fixed 28-day cycle. With only one or two logged cycles, we work with what's available; the more logged, the more the forecast reflects the actual pattern.
From that cycle length, we estimate where each phase is likely to fall — menstrual, follicular, ovulation, luteal, and PMS — based on established research into typical cycle-phase timing.
Ovulation itself happens in a 12-24 hour window, but conception is biologically possible across many days. Sperm can survive in the body for several days before ovulation, and the egg remains viable for a time afterward, so the days that carry some chance of conception extend beyond ovulation itself in both directions.
We anchor our ovulation approximation 13 days before the predicted next period, a widely supported general rule, and we display it across several days rather than a single date, since no calendar-based estimate can identify the exact day of ovulation with certainty.
This uncertainty is real, and worth being direct about: Lunarmates' ovulation and fertility estimates should never be used as a method of contraception or to plan a pregnancy. Methods that incorporate biological signals — such as basal body temperature, ovulation test results, or cervical mucus changes — can signal ovulation considerably more accurately than calendar-based estimates alone.[1] Lunarmates does not collect this kind of biometric data; we work only from the dates that are logged, by design, to keep the app simple and the data we hold to a minimum. If precise fertility timing matters to you, a method that incorporates biological markers, ideally alongside guidance from a healthcare provider, will serve you better than any calendar-based app, including ours.
If a predicted period date passes and a cycle start has not been logged, we try to stay on track but can't keep on presenting that guess as settled fact. Once enough time has passed relative to the averaged cycle length, we mark the cycle as overdue.
Separately, you may see check-in reminders earlier than that. Cycles naturally vary, so an early reminder simply means it's just checking in, not that anything is wrong.
We are building a curated library of articles and references that inform the Lunarmates approach. Check back soon.
[1] Worsfold, L., Marriott, L., Johnson, S., & Harper, J. C. (2021). Period tracker applications: What menstrual cycle information are they giving women? Women's Health, 17, Article 17455065211049905. https://doi.org/10.1177/17455065211049905