The ovulation period calculator helps you determine your most fertile days based on your last period date and cycle length. Last Period Date Menstrual Cycle Length (Days) 20 days 21 days 22 days 23 days 24 days 25 days 26 days 27 days 28 days 29 days 30 days 31 days 32 days 33 days 34 days 35 days 36 days 37 days 38 days 39 days 40 days 41 days 42 days 43 days 44 days 45 days Luteal Phase Length (Days) 10 days 11 days 12 days 13 days 14 days 15 days 16 days 17 days 18 days 19 days 20 days Calculate Clear Please select your last period date. Estimated Next Period Date Estimated Ovulation Day Fertile Window Start Fertile Window End Most Fertile Days Earliest Date for Pregnancy Test Your chances of conceiving are highest during these dates. Ovulation typically occurs on this date.