When you open LunaList, the top of the screen shows a few sentences. We call it the daily summary. This post explains how it’s built, where we use AI, and where we don’t.

Every summary has four parts#

The summary tells you one thing about today and shows the reason straight away. If any of the four parts is missing, the app doesn’t show the summary at all.

Where

Cycle day 23

What

You might feel a bit tired over the next few days.

Why

In your last 3 cycles you logged tiredness between days 22 and 26.

Based on

Your 3 cycles · 14 logs

  • Where: which phase of your cycle you're in, and which day.
  • What: the main sentence for today or the next few days.
  • Why: which of your logs led to that conclusion.
  • Source: what it rests on, meaning how many of your cycles and logs, or a medical source.

Your normal is your own history#

The summary is calculated from your logs, not from a textbook table. That turns into a few rules:

  • 28 days is never shown as the norm. You're compared with your own average.
  • Dates are always shown as a range: “Oct 11-15, most likely the 13th”. Never a single date.
  • When there’s little information, the summary says so: “still an estimate”.
  • A red warning appears only when seeing a doctor is advised. A late period is not an alarm.

Where AI comes in#

The summary isn’t written by AI. The app’s own rules calculate it from your logs. AI appears in one place only: the morning “Today’s tip” notification. It’s written by Google Gemini, and this is what gets sent:

  • Your symptom, mood and sleep logs from the last 7 days
  • Your cycle day and phase, and the length of your recent cycles
  • Your goal, plus age and weight if you've added them to your profile
  • Your name, email and phone number are not sent.

It isn't a chat. There's no way to ask Gemini questions or talk to it. If Gemini doesn't respond, you get a ready-made tip for your goal instead. Don't want the notification? Notification settings → Health tips.

Where is your information?#

Your logs are stored on our servers, linked to your account, so your history survives a device change. They're encrypted in transit with TLS, never sold and never shared for advertising. Which service receives what is listed in section 4 of our Privacy Policy.

Privacy Policy

Few words. Each one with a reason.