Period & Fertility Calendar
100% private period & ovulation tracker. Enter your last period date & cycle length to get a 6-month fertility forecast, ovulation day, fertile window, and pregnancy chance indicator. All data stays in your browser.
How to use
- 1Enter the first day of your last period
- 2Set your average cycle length (21–45 days, default 28)
- 3Set your typical period duration (2–10 days, default 5)
- 4View the color-coded calendar: red = period, purple = ovulation, blue = fertile window
- 5Check the status dashboard for today's phase and days until next period
- 6Your settings are automatically saved in your browser for next time
Frequently Asked Questions — Period & Fertility Calendar
How do you calculate ovulation day?+
Ovulation typically occurs 14 days before the start of the next period. Formula: Ovulation Day = Next Period Start Date − 14 days. For a 28-day cycle, this is day 14. For a 30-day cycle, this is day 16. This is based on the luteal phase being approximately 14 days for most women.
What is the fertile window?+
The fertile window spans 6 days: the 5 days before ovulation plus the day of ovulation itself. Sperm can survive in the female reproductive tract for up to 5 days, which is why the days before ovulation are also fertile. The egg can only be fertilized within 12–24 hours of ovulation.
Is this period tracker completely private?+
Yes. All your data is stored exclusively in your browser's localStorage. No data is sent to any server, no account is required, and no tracking occurs. You can clear your data at any time by clearing your browser cache or using the reset button in the tool.
How accurate is a calendar-based period tracker?+
Calendar methods are most accurate for women with regular cycles. The key limitation is that ovulation can shift due to stress, illness, travel, or hormonal changes. For contraception, calendar methods alone are not recommended as a sole method. For conception, track additional signs like basal body temperature (BBT) and cervical mucus for better accuracy.