Find your most fertile days with our free ovulation calculator. Enter the first day of your last period and your average cycle length to estimate when you’re most likely to ovulate — and your best window for conception.
Ovulation & Fertility Calculator
Understanding Your Fertile Window
Ovulation typically occurs about 14 days before your next period, regardless of cycle length. In a 28-day cycle that’s day 14; in a 32-day cycle it’s around day 18. Your fertile window spans roughly 6 days — the five days before ovulation (sperm can survive up to 5 days) and the day of ovulation itself.
Ovulation Timing by Cycle Length
- 24-day cycle: Ovulation around day 10
- 28-day cycle: Ovulation around day 14
- 30-day cycle: Ovulation around day 16
- 35-day cycle: Ovulation around day 21
Frequently Asked Questions
When do I ovulate?
Most women ovulate about 14 days before their next period. For a 28-day cycle, that’s around day 14. For a 35-day cycle, it’s around day 21. Ovulation can vary by several days each month based on stress, illness, and other factors.
How long does ovulation last?
The egg is only viable for 12–24 hours after release. However, sperm can survive in the reproductive tract for up to 5 days, which is why the fertile window extends 5 days before ovulation. The total fertility window is therefore about 6 days per cycle.
What are signs of ovulation?
Common signs include a slight rise in basal body temperature (0.2–0.5°C), cervical mucus becoming clear and stretchy (like raw egg whites), mild one-sided pelvic pain (mittelschmerz), and a surge in luteinizing hormone (LH) detectable by ovulation predictor kits (OPKs).
Can I get pregnant outside the fertile window?
It is very unlikely but not impossible, especially if your cycle is irregular and ovulation occurs at an unexpected time. The calculator provides estimates based on average cycle patterns — not a guarantee.
Does stress affect ovulation?
Yes. Physical or emotional stress can delay or suppress ovulation by affecting hormone levels. Illness, extreme exercise, significant weight changes, and disrupted sleep can also shift your ovulation date, making cycle tracking more complex.