Ovulation Calculator
Calculate your ovulation date and fertile window based on your menstrual cycle. Understand your cycle and optimize your chances of conception.
How to Use This Calculator
- Enter the first day of your last menstrual period.
- Enter your typical cycle length (20–45 days, default 28).
- Click Calculate to see your ovulation date, fertile window, and next period.
Formula
Ovulation is the release of an egg from the ovary, typically occurring 14 days before the next period (the luteal phase is usually 12–16 days, with 14 being the standard assumption). The fertile window spans 6 days: the 5 days before ovulation plus ovulation day itself, since sperm can survive up to 5 days and the egg is viable for about 24 hours.
Cycle Irregularity: If your cycle varies month to month, this calculator provides an estimate. For irregular cycles, tracking basal body temperature or using ovulation predictor kits may give more accurate results.
Examples
Ovulation: Jan 15. Fertile Window: Jan 10 – Jan 15. Next Period: Jan 29.
Ovulation: Mar 21. Fertile Window: Mar 16 – Mar 21. Next Period: Apr 4.
Ovulation: Jun 22. Fertile Window: Jun 17 – Jun 22. Next Period: Jul 6.
Frequently Asked Questions
When do I ovulate?
You typically ovulate 14 days before your next period begins. For a 28-day cycle, this is around day 14. For shorter or longer cycles, the ovulation day shifts accordingly, but the luteal phase (post-ovulation) remains relatively constant at 12–16 days.
How long is the fertile window?
The fertile window is approximately 6 days: the 5 days before ovulation and ovulation day itself. Sperm can survive in the reproductive tract for up to 5 days, while the egg is viable for 12–24 hours after release.
Can I get pregnant outside the fertile window?
It is extremely unlikely but not impossible. Sperm survival and ovulation timing can vary slightly between individuals. For most people, pregnancy can only occur within the 6-day fertile window.