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
Period tracker apps often assume every woman has a textbook 28-day cycle with ovulation on day 14 — a big part of why Lunarmates treats every cycle, and every day within it, as different rather than fixed.
[2] Reberte, L. M., de Andrade, J. H., Hoga, L. A. K., Rudge, T., & Rodolpho, J. R. C. (2014). Men's perceptions and attitudes toward the partner with premenstrual syndrome. American Journal of Men's Health, 8(2), 137–147. https://doi.org/10.1177/1557988313497050
Men who understand the biological basis of premenstrual changes related to their partners with more empathy and less confusion — research the authors say has the potential to "improve gender relations." Links to Lunarmates' "understanding, not managing" design.
[3] García-Egea, A., Jacques-Aviñó, C., Berenguera, A., Baroja-Benlliure, J., Pinzón-Sanabria, D., Holst, A. S., López-Jiménez, T., Munrós-Feliu, J., Vicente-Hernández, M. M., Valls-Llobet, C., Martínez-Bueno, C., & Medina-Perucha, L. (2025). “If everyone comes together, many things can be changed”: A qualitative study on men's perspectives on menstrual health and equity in the Barcelona area (Spain). PLOS ONE, 20(2), e0312685. https://doi.org/10.1371/journal.pone.0312685
Most men learn what little they know about menstruation directly from a partner, with little to no formal education and notes that "men should raise awareness of a more positive stance on menstruation."
[4] Farage, M. A., Neill, S., & MacLean, A. B. (2009). Physiological changes associated with the menstrual cycle: A review. Obstetrical & Gynecological Survey, 64(1), 58–72. https://doi.org/10.1097/OGX.0b013e3181932a37
Reviews the hormonal changes across the menstrual cycle and their measurable physical and emotional effects — the biological basis for why Lunarmates treats the cycle as a real physiological pattern worth tracking, not just a mood.
[5] Ronca, F., Blodgett, J. M., Bruinvels, G., Lowery, M., Raviraj, M., Sandhar, G., Symeonides, N., Jones, C., Loosemore, M., & Burgess, P. W. (2025). Attentional, anticipatory and spatial cognition fluctuate throughout the menstrual cycle: Potential implications for female sport. Neuropsychologia, 206, 108909. https://doi.org/10.1016/j.neuropsychologia.2024.108909
Found that women's self-reported symptoms during menstruation didn't match their actual performance, which was often better — a reminder that self-report and what's really happening can diverge, part of why Lunarmates favors sharing plain forecast data to help men generate observations.
[6] Farage, M. A., Osborn, T. W., & MacLean, A. B. (2008). Cognitive, sensory, and emotional changes associated with the menstrual cycle: A review. Archives of Gynecology and Obstetrics, 278(4), 299–307. https://doi.org/10.1007/s00404-008-0708-2
Confirms that cyclic hormonal changes have measurable effects on cognition, emotion, and sensory processing — supporting Lunarmates' premise that a partner's mood shifts follow a real, predictable biological pattern.