Calculate your next ovulation date, fertile window and next period based on your cycle.
Enter the first day of the last period and usual cycle length, then calculate the estimated fertile window, ovulation day and next period.
Ovulation does not occur on exactly the same cycle day for everyone and can shift from month to month.
The calculator estimates ovulation from the start of the last period and the usual cycle length. Calendar methods commonly place ovulation around the latter part of a cycle, but real cycles are not clockwork. Stress, illness, travel, breastfeeding, perimenopause and hormonal changes can move ovulation earlier or later.
Treat the displayed fertile window as a planning range rather than confirmation that ovulation occurred on a particular day. People trying to identify ovulation more closely may combine calendar estimates with cervical mucus changes, basal-body-temperature tracking or ovulation tests. This calculator is not a contraceptive method and should not be relied on by itself to prevent pregnancy. If cycles are persistently irregular or fertility is a concern, a clinician can assess factors a date calculator cannot see.