Ovulation & Fertility Calculator

What is Ovulation & Fertility Calculator?

The Ovulation & Fertility Calculator identifies your 6-day fertile window, peak ovulation day, and most fertile conception dates based on the first day of your last menstrual period and average cycle length. It also estimates upcoming period dates and pregnancy test timing with zero data transmission.

Designed for accuracy, speed, and privacy, this tool runs entirely on your local device with zero network latency.

How to Use the Ovulation & Fertility Calculator

1. 1
   Select the first day of your most recent menstrual period in the date picker.
2. 2
   Enter your average menstrual cycle length in days (typically 21 to 35 days, default 28).
3. 3
   Optionally customize your luteal phase duration (default is 14 days).
4. 4
   Inspect your fertile window calendar, peak fertility days (star icon), next period date, and earliest pregnancy test date.

Formula & Calculation Logic

Calculates the expected ovulation day by subtracting the luteal phase (typically 14 days) from the total cycle length, establishing the 6-day biological fertile window based on sperm longevity (up to 5 days) and ovum lifespan (12–24 hours).