Ovulation Calculator — Find Your Fertile Window
The Ovulation Calculator estimates the day of ovulation and your fertile window based on the first day of your last menstrual period and the length of your cycle. Ovulation typically occurs 14 days before the next period. Your fertile window spans the 5 days before ovulation plus the day of ovulation itself — giving 6 days when conception is possible.
How to Use This Calculator
- 1
Enter the year, month, and day your last period started.
- 2
Enter your average cycle length (default is 28 days).
- 3
Click Calculate to see how many days until your estimated ovulation day.
- 4
Your fertile window begins 5 days before ovulation.
Frequently Asked Questions
Ovulation typically occurs 14 days before the start of the next period. For a 28-day cycle, this is around day 14. For a 30-day cycle, it would be around day 16.