Everything stays on this phone. No account, no cloud, no one else.
You can change all of this later.
Luna uses your real average once you've logged two or more periods.
Usually 14. Only change if a doctor told you otherwise.
Everything is stored on this device only. Save a backup file before changing phones.
Luna is for tracking, not medical advice or birth control.
Luna is a free, private cycle and ovulation tracker that runs entirely in your browser. No account, no cloud, no tracking — your data stays on your device. Track your period, predict ovulation, log symptoms and mood, and see your cycle patterns over time. Everything is saved locally, so you can close the tab and come back without losing anything.
Unlike most period tracking apps, Luna does not require a sign-up, does not send your data to a server, and does not show ads within the tracking interface. Your cycle information is some of the most personal data you have, and Luna is designed to keep it that way — private, on your device, under your control. You can export a backup file at any time and restore it on a new device.
Getting started takes about 30 seconds. Enter the first day of your last period, your usual cycle length (the default is 28 days), and how many days your period typically lasts. Luna immediately calculates your predicted ovulation date, fertile window, and next period start. As you log more periods, the predictions get smarter — Luna switches from your default cycle length to your real average after two cycles.
To log a period, tap the "Period started today" button on the Today screen. To log symptoms, mood, flow, or notes for any day, tap that day on the calendar. A bottom sheet opens with chips for flow level (spotting, light, medium, heavy), mood (great, calm, tired, iritable, and more), symptoms (cramps, headache, bloating, and more), and a free-text note field. Tap Save and your day is logged.
The Today screen shows a beautiful circular dial with your current cycle day, phase (menstrual, follicular, fertile, ovulation, or luteal), and a visual arc showing where you are in your cycle. The calendar view color-codes each day: solid rose for logged period days, dashed border for predicted period days, green for fertile days, and amber for ovulation.
Your menstrual cycle has four main phases. The menstrual phase (your period) typically lasts 3-7 days and marks the start of a new cycle. The follicular phase follows, during which your body prepares an egg for release — this is usually when energy levels are highest. Ovulation occurs around the middle of your cycle, typically 14 days before your next period starts, and marks the most fertile day. The luteal phase is the final stretch before your next period, often accompanied by PMS symptoms like bloating, mood changes, and fatigue.
Luna identifies your fertile window as the 5 days before ovulation plus the day of ovulation itself, since sperm can survive up to 5 days in the reproductive tract. This is the time when pregnancy is most likely. Luna uses your luteal phase length (default 14 days) to work backward from your predicted next period to estimate ovulation, which is more accurate than simply assuming day 14 of your cycle.
Cycle tracking data is deeply personal. Many period tracking apps upload your data to cloud servers, where it can be used for advertising, sold to third parties, or exposed in a data breach. Luna takes a different approach. Everything — your period dates, symptoms, moods, notes, and settings — is stored in your browser's localStorage, which means it lives only on your device. There is no server, no database, no account, and no tracking. You can verify this yourself by opening your browser's developer tools and inspecting the localStorage.
The trade-off is that your data is tied to this browser on this device. If you clear your browsing data, your cycle history will be erased. That is why Luna includes a backup feature — export your data to a JSON file, store it somewhere safe, and restore it whenever you need. This gives you full control over your data without relying on a cloud service you cannot audit.
Yes, Luna is completely free. There are no premium tiers, no subscriptions, and no in-app purchases.
No. Luna stores all your cycle data locally in your browser using localStorage. Nothing is uploaded to any server. Your data never leaves your device.
No account is needed. Just open the page, enter your last period date, and start tracking. Your data is saved on your device automatically.
Yes. Luna uses your cycle length and luteal phase to estimate your fertile window and ovulation date. The predictions improve as you log more periods.
Yes. Luna has a backup feature that lets you export all your data as a JSON file and restore it on another device.
No. Luna is for tracking and awareness only. It is not medical advice or a form of birth control. Always consult a healthcare provider for medical decisions.