Help
How estimates work
Luna is a simple cycle awareness tool. It does not diagnose conditions, predict pregnancy, or replace medical care.
1
What you enter
- Last period start date (required)
- Optional earlier period starts
- Typical cycle length and period length
2
What Luna calculates
- Next period: last start plus your cycle length
- Period days: the first N days of each cycle
- Fertile window: around estimated ovulation (about 14 days before the next period), roughly 6 days
- Lower fertility awareness days: outside period and fertile window
3
Privacy
All data stays in your browser’s local storage on this device. There is no account and no server sync.
Important
Estimates only. Based on calendar averages, not ovulation tests or medical data. Not birth control and not medical advice. Cycles vary; when in doubt, talk to a clinician.
Ready to check your cycle?
Open the app, enter a few dates, and see today’s phase on this device.