This ovulation calculator is able to predict the most fertile days in your menstrual cycle and exactly when you should conceive for a certain due date. You can read below the form about conception, ovulation and other facts on the menstrual cycle.

The first day of your last menstrual period: *
Menstrual cycle length: *

How does this ovulation calculator work?

This useful health tool can determine the most fertile days and the corresponding due date in case of the fertilization of the egg. In order to do so, you are asked to input the data of your menstrual cycle that is the length and the first day of the latest period.

The result is going to comprise the data for the current cycle, such as the most fertile days as well as the estimated due dates in case of conception, plus an ovulation calendar for the next 12 months that tell exactly when the fertile window is going to be, the estimated due date if needed and the following period start.

Example ovulation calculation and result

Let’s take for instance the case of a woman with a cycle length of 31 and the first day of the period August 27th 2014. Her result would be:

Based on your last period starting at August 27, 2014 the results are:

■ Your next menstrual period is most likely to start on September 27, 2014;

■ You next most fertile days are between September 11, 2014 and September 15, 2014;

■ If you conceive within these most fertile days September 11 - September 15, 2014 your estimated due date will be June 06, 2015.

■ This is the ovulation calendar for the next 12 months: (3 months depicted in the example):

Period start Most fertile days Next Period Start Estimated due date
Aug 27, 2014 Sep 11 - Sep 15, 2014 Sep 27, 2014 Jun 06, 2015
Sep 27, 2014 Oct 12 - Oct 16, 2014 Oct 28, 2014 Jul 07, 2015
Oct 28, 2014 Nov 11 - Nov 15, 2014 Nov 27, 2014 Aug 07, 2015

Menstrual cycle

The menstrual cycle defines the changes in the female body when is being prepared for reproduction. For that is essential for the ovaries to produce eggs and for the uterus to be ready to host an embryo.

A woman's first menstruation occurs around the age 13 and is called menarche. The end of a woman's reproductive period is called menopause and occurs between the ages of 45 and 55.

The menstrual cycle occurs in fertile females every 28 days, in average. The length may vary between 26 and even 34 days. Each cycle consists of three different phases, controlled by the endocrine system: follicular phase, ovulation and luteal phase. 


By convention, each menstrual cycle is considered to begin from the first day of menstrual bleeding. In the first phase, follicles in the ovary begin developing and after several days, approximately in the middle of the cycle, one of them is mature enough to be released from the ovary. Event called ovulation.

So the probable ovulation date that the ovulation calculator shows is the moment, half way through the menstrual cycle, in which the female body releases a mature egg from the ovary, egg that can be fertilized if it meets a male sexual cell.

If the fertilization occurs, the egg will implant in the uterus lining and continue developing in the future new born. If fertilization does not happen, the uterus will shed its lining and egg in about two weeks after the ovulation, causing the bleeding period called menstruation.

The possible conception dates represents the most fertile period of time in which if a sexual intercourse occurs the egg is most likely to be fertilized and generate a pregnancy. This period of time covers from about 5 days before ovulation until 1-2 days after ovulation.


1) 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

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

24 Dec, 2014