Ovulation Calculator
Estimate your fertile window and ovulation day based on your last menstrual period and cycle length.
Results
What is it?
Ovulation is the release of a mature egg from the ovary. It typically occurs 14 days before your next expected period. The fertile window — the days you can conceive — spans the 5 days before ovulation (because sperm can survive up to 5 days in the female reproductive tract) through approximately 24 hours after ovulation (the lifespan of a released egg).
How to use
1. Enter your average cycle length (count from day 1 of one period to day 1 of the next). 2. Enter the calendar day of the month your last period began. 3. The calculator shows your estimated ovulation day and fertile window for this cycle. 4. For higher precision, track basal body temperature (BBT) or use LH ovulation predictor kits (OPKs).
Example scenario
LMP started on the 5th of the month, cycle is 30 days. Ovulation = 5 + 30 - 14 = day 21. Fertile window: days 16-22. Next period expected around day 35 (i.e. the 5th of the following month).
Pro tip
Ovulation timing varies even in regular cycles. Stress, illness, travel, and intense exercise can shift ovulation by several days. If you are trying to conceive (or avoid pregnancy), combine calendar tracking with BBT charting and OPKs for the most reliable prediction.