Ovulation Calculator

Ovulation usually happens about 14 days before the next period (ACOG); this calculator subtracts the days from ovulation to your next period (default 14) from your cycle length. The fertile window shown is the 6-day interval ending on the estimated day of ovulation (ASRM), which also describes the calendar method used here: ovulation is set at cycle length minus a luteal phase of about 14 days. These are estimates from calendar dates, not a measurement of ovulation. This tool is not a contraception method and does not guarantee pregnancy. Cycle irregularity is common; consult a gynaecologist if cycles are very irregular.