Free Ovulation Calculator — Find Your Fertile Window
Estimate your fertile window and ovulation day. Uses the calendar method based on your cycle length.
How Is Ovulation Calculated?
The calendar method estimates ovulation by subtracting 14 days from the expected start of your next period. For a 28-day cycle, ovulation typically occurs on day 14. The fertile window spans approximately 5 days before ovulation through the day of ovulation.
What Affects Ovulation Timing?
Stress, illness, travel, and significant weight changes can delay or advance ovulation. For the most accurate tracking, combine the calendar method with basal body temperature (BBT) charting and cervical mucus observation.
Frequently Asked Questions
How do I know when I am ovulating?
In addition to the calendar method, watch for: changes in cervical mucus (becomes clear and stretchy), a slight rise in basal body temperature, mild pelvic pain (mittelschmerz), and increased libido.
Can I get pregnant on any day of my cycle?
Pregnancy is only possible during the fertile window — approximately 5 days before ovulation and the day of ovulation itself. However, cycle variations mean this window can be difficult to predict precisely.
What if I have long or short cycles?
Adjust the cycle length in the calculator. For a 35-day cycle, ovulation typically occurs around day 21 (35-14=21). For a 21-day cycle, around day 7.