Ovulation Calculator

Predicts the fertile window and ovulation day based on menstrual cycle, to help with conceiving.

The first day of your last menstrual period:
Menstrual cycle length:
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Steps on how to print your input & results:

1. Fill in the calculator/tool with your values and/or your answer choices and press Calculate.

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.

This ovulation calculator uses the first day of the last menstrual cycle and the cycle length to determine the most fertile days during that cycle, the probable ovulation date and an estimated due date in case conception occurs during the most fertile days.

The calculator also offers an ovulation calendar, with similar information for the next 12 cycles.

Please note the probable ovulation date is set half-way through the menstrual cycle and the fertile window is set between 5 days before and 2 days after ovulation.

The possible estimated due date is set at approximately 266 days from possible conception date.


Wilcox AJ, Baird DD, Weinberg CR. (1999) Time of implantation of the Conceptus and loss of pregnancy. New England Journal of Medicine 340 (23): 1796–1799

Beckmann CRB. (2010) Obstetrics and Gynecology. Lippincott Williams & Wilkins. pp. 306–307

Specialty: Obstetrics Gynecology

System: Reproductive

Article By: Denise Nedea

Published On: April 13, 2020

Last Checked: April 13, 2020

Next Review: April 13, 2025