Ovulation & Fertile Days Calculator
This tool estimates your expected ovulation day and fertile window (the best days to conceive) from the first day of your last period and your cycle length. Ovulation usually occurs 14 days before your next period. Results assume a regular cycle; if your cycle is irregular or conception takes over a year (or 6 months after age 35), see an OB-GYN.
Medical disclaimer: This tool is for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
Frequently asked questions
When does ovulation occur?
Usually 14 days before the next period. In a regular 28-day cycle that is around day 14 from the start of your period; the day shifts as cycle length changes.
What is the fertile window?
About 6 days ending with ovulation day plus one day after — sperm survive up to 5 days while the egg lives about 24 hours, so the 3 days before ovulation offer the highest chance.
My cycle is irregular — does the calculator work?
Accuracy drops. Track ovulation signs (clear stretchy discharge, mild one-sided pain) or use ovulation test strips, and see an OB-GYN to evaluate the irregularity.