This fertility calculator keeps track of the ovulation and most fertile days throughout your menstrual cycle for the following 12 months. You can read more about ovulation and conception times below the form.

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

How does this fertility calculator work?

This health tool can help you keep track of the fertile days and of the period days in your menstrual cycle.

This fertility calculator takes account of the first day of your last menstrual period, the menstrual cycle length and the length of the period.

As you provide this data, by simply pressing the “Calculate” button the form will display you personalized information for the next 12 menstrual cycles on terms of the most fertile days, period start and period end.

What are the fertile days of the menstrual cycle?

In order to establish what is the fertile period we need to discuss some basic information on the menstrual cycle. This cycle can take from 26-36 or more days and represents a cycle of maturation for an ovule in the female’s body.

The first 3-7 days in the cycle are most recognized because they bring the menstrual bleeding also known as the period. In about two weeks an important event takes place: the ovulation.

The ovulation represents the time when an ovule ready to be fertilized is released from the ovary. If the ovule is fertilized it will later fix itself in the uterus and develop in a pregnancy. If not then another menstrual bleeding will take place in exactly 14 days from the ovulation date.

What there is to be mentioned is that the period of time before the ovulation can vary according to the length of the cycle while the period of time after the ovulation is always 14 days.

The fertile days represent an “open window” around the ovulation date in which there are the highest chances for the ovum to be fertilized.

This fertility calculator uses a window of two days before and two days after the ovulation date for the fertile days for a better precision. Some consider that this amount of time should include around 4 days before and after the ovulation date.

Tracking the menstrual cycle and the signs of ovulation can prove to be useful for both the situation in which someone wants to get pregnant or to avoid pregnancy.

However, this method of the calendar should not be used as an unique contraceptive method as the female body does not always work as a clock and stress, hormones and other factors can influence the menstrual cycle.

Example of a fertility calculation and result:

For a cycle length of 29 days and the latest period starting on the 5th of November 2014 this is the result:

Based on your last period starting at November 5, 2014 and having a length of 4 days, the results are:

Your next menstrual period is most likely to start on December 4, 2014;

You next period will end on December 7, 2014;

This is the Period calendar for the next 12 months:

Period start Period end Most fertile days
Dec 4, 2014 Dec 7, 2014 Dec 17 - Dec 21, 2014
Jan 2, 2015 Jan 5, 2015 Jan 15 - Jan 19, 2015
Jan 31, 2015 Feb 3, 2015 Feb 13 - Feb 17, 2015
Mar 1, 2015 Mar 4, 2015 Mar 14 - Mar 18, 2015
Mar 30, 2015 Apr 2, 2015 Apr 12 - Apr 16, 2015
Apr 28, 2015 May 1, 2015 May 11 - May 15, 2015
May 27, 2015 May 30, 2015 Jun 9 - Jun 13, 2015
Jun 25, 2015 Jun 28, 2015 Jul 8 - Jul 12, 2015
Jul 24, 2015 Jul 27, 2015 Aug 6 - Aug 10, 2015
Aug 22, 2015 Aug 25, 2015 Sep 4 - Sep 8, 2015
Sep 20, 2015 Sep 23, 2015 Oct 3 - Oct 7, 2015
Oct 19, 2015 Oct 22, 2015 Nov 1 - Nov 5, 2015


1) Young B. (2006) Elsevier Health Sciences.

2) Wilcox AJ, Baird DD, Weinberg CR (1999) . New England Journal of Medicine 340 (23): 1796–1799

15 Dec, 2014