Find your most fertile days based on your menstrual cycle length.
Calculate your fertile window instantly.
Ovulation typically occurs about 14 days before your next period starts, regardless of your total cycle length. Your fertile window includes the five days before ovulation plus the day of ovulation itself.
This is because sperm can survive in the reproductive tract for up to five days, while the egg is only viable for about 12-24 hours after release — making the days leading up to ovulation the most fertile.
Ovulation Date = Next Period Start Date − 14 days
Fertile window = 5 days before ovulation + ovulation day
Tracking these signs alongside calendar predictions gives a more accurate picture than dates alone, especially for irregular cycles.
This calculator works best with regular cycles. For irregular cycles, tracking physical ovulation signs or using ovulation predictor kits may give more reliable results.
The egg is typically viable for only 12-24 hours after release, which is why timing intercourse in the days leading up to ovulation is often recommended.
It's unlikely but not impossible, especially with cycle variability. The fertile window represents the highest probability days, not an absolute limit.