The Ovulation Calculator estimates the likely ovulation date from the first day of the last menstrual period and an average cycle length. The model places ovulation about 14 days before the next expected period and displays an estimated fertile window from five days before through one day after ovulation. Calendar estimates are less reliable when cycles vary, after stopping hormonal contraception, during breastfeeding, or with conditions that affect ovulation.
Enter day 1 of the most recent menstrual bleeding.
Use an average from several recent cycles when possible.
The main result is the estimated ovulation date.
The displayed fertile window is a planning estimate, not confirmation of ovulation or reliable contraception.
This calendar model uses the relatively more consistent interval between ovulation and the next period, but individual cycles vary.
The dates identify a likely interval when conception may be possible, not a diagnosis or guarantee.
Ovulation tests, cervical mucus observations, basal temperature patterns, or clinical monitoring can provide additional information.
Given: Last period began August 1, 2026 and the average cycle is 28 days.
Calculation: Next period is estimated for August 29. Subtracting 14 days gives estimated ovulation on August 15.
Result: The estimated fertile window is August 10 through August 16.
No calendar estimate is reliable enough to guarantee pregnancy prevention. Use an effective contraceptive method and professional guidance.
The estimate may be substantially less accurate. Tracking several cycles and discussing irregularity with a clinician may be appropriate.
Sperm may survive for several days and an egg remains viable for a shorter time after ovulation, so fertility spans more than one date.
Not always. An ovulation predictor test detects a hormone rise that often precedes ovulation and may shift the estimate.
Seek clinical guidance for concerns about absent or highly irregular periods, fertility, pregnancy symptoms, pain, or unusual bleeding.