This page exists to be honest about what Luna is, what it isn't, and how it works under the hood. No fine print. No weasel words. We wrote this because legal polish is easy, but real transparency means telling you what we don't know.
Luna is a free, open-source menstrual cycle tracking companion. You log your cycles by talking to an AI assistant — type things like "my period started today" or "I'm feeling crampy" and Luna records it. Over time, it learns your patterns and predicts when your next period might come.
The prediction engine uses adaptive exponential smoothing with 10 condition-specific population priors. It starts with research-based averages that differ depending on your health conditions (PCOS 51d, endometriosis 27d, thyroid 35d, etc.), then learns from your actual cycles. The more cycles you log, the more it trusts your data over the population averages.
Luna is open source under the MIT license. You can read every line of code that handles your data and makes predictions. The full pipeline — database schema, prediction algorithm, AI tool definitions, API routes — is in one GitHub repository. Nothing is hidden.