Ovulation Calculator
Estimated ovulation, fertile window and next six periods on a calendar.
About this tool
Enter the first day of your last period, your average cycle length, period length and, if you know it, your luteal phase. You see the estimated ovulation date, the fertile window, the next period with a countdown, today's cycle day, and a four-month calendar with periods, fertile days and ovulation marked.
How ovulation is estimated
Ovulation happens about one luteal phase before the next period. The luteal phase โ from ovulation to the next period โ is fairly constant for each person, usually 12โ16 days with 14 as the average, while the first half of the cycle varies. So in a 28-day cycle ovulation is around day 14, and in a 32-day cycle around day 18. The fertile window is the five days before ovulation plus the day itself, because sperm can survive up to about five days and an egg about one. If you have tracked your cycle with ovulation tests or temperature charts, entering your own luteal phase makes the estimate better. Important: cycles shift month to month with stress, illness and travel, and a calendar only predicts โ it cannot detect ovulation. That is why this must not be used as contraception, and why people trying to conceive often confirm with LH test strips or basal body temperature. General information, not medical advice; talk to a doctor or nurse about irregular cycles. Nothing is stored or sent. The pregnancy due date calculator takes over from a positive test, the date difference calculator counts days, and the calendar prints months.
Frequently asked questions
When am I most fertile?
In the two or three days before ovulation and on the day itself. The full fertile window is about six days ending on ovulation day.
Can I use this as birth control?
No. Calendar estimates are wrong often enough that they are not reliable contraception. Use a proven method and speak to a clinician.
What if my cycles are irregular?
Use your average cycle length, but expect the estimate to be less reliable. Ovulation tests or temperature tracking give a much better picture.
Is my information saved?
No. Dates are calculated in your browser and nothing is stored or sent.