This period calculator is a useful tool that can keep track of the menstrual cycle period dates in the following 12 months. You can read more below the form on the most important menstrual cycle days and on the fertility times.

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

Disclaimer: Please note this returns only an estimation of your menstrual cycle should not be relied upon for reproductive health purposes.

How does this period calculator work?

This great tool can determine the most important data of your cycle for you, from the fertile days to the period days in your menstrual activity.

The period 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 and you can change the data input for as many times as you want with the reset button.

Example period calculation and result:

For a menstrual cycle length of 31 days, period length of 4 days and the latest period starting on November 15th 2014:

Based on your last period starting at November 15, 2014 and having a length of 4 days, the results are:

■ Your next menstrual period is most likely to start on December 16, 2014;

■ You next period will end on December 19, 2014;

■ This is the Period calendar for the next 12 months:

 Period start   Period end   Most fertile days 
 Dec 16, 2014   Dec 19, 2014   Dec 31 - Jan 4, 2015 
 Jan 16, 2015   Jan 19, 2015   Jan 31 - Feb 4, 2015 
 Feb 16, 2015   Feb 19, 2015   Mar 3 - Mar 7, 2015 
 Mar 19, 2015   Mar 22, 2015   Apr 3 - Apr 7, 2015 
 Apr 19, 2015   Apr 22, 2015   May 4 - May 8, 2015 
 May 20, 2015   May 23, 2015   Jun 4 - Jun 8, 2015 
 Jun 20, 2015   Jun 23, 2015   Jul 5 - Jul 9, 2015 
 Jul 21, 2015   Jul 24, 2015   Aug 5 - Aug 9, 2015 
 Aug 21, 2015   Aug 24, 2015   Sep 5 - Sep 9, 2015 
 Sep 21, 2015   Sep 24, 2015   Oct 6 - Oct 10, 2015 
 Oct 22, 2015   Oct 25, 2015   Nov 6 - Nov 10, 2015 
 Nov 22, 2015   Nov 25, 2015   Dec 7 - Dec 11, 2015 

Menstrual cycle

For every woman it is very important to keep track of her menstrual cycle dates in order to notice the existence of a pattern and so to know exactly what is happening with her body at each time of the month.

Knowing when the next period will start is important so you are always ready as it is also important to know when are the most fertile days of the menstrual cycle no matter if you are trying to get pregnant or to avoid a pregnancy or simply to recognize your bodily signs due to hormonal changes.

This period calculator provides you with a 12 months prognosis of your next 12 menstrual cycles including the first period day, the last period day and the fertile window. This can help you plan your life and not worry for the next period, the days when you’re most fertile or an eventual late period.

In order to understand how it works here is some basic information about the menstrual cycle and the most fertile days. The menstrual cycle occurs in fertile females every 28 days, in average. The length may vary between 26 and even 36 days. Each cycle consists of three different phases, controlled by the endocrine system: follicular phase, ovulation and luteal phase. 

The bleeding period of the menstrual cycle is usually called period and has a length varying from 2-9 days and different blood debits in each woman. The bleeding happens if fertilization does not occur in the previous menstrual cycle and the uterus sheds its lining and egg in about two weeks after the ovulation.


Ovulation represents the moment when a matured follicle is released from the ovary and ready to be fertilized. If the fertilization occurs, the egg will implant in the uterus lining and continue developing in the future new born.

The form also displays the fertile days which are the possible conception dates 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. 

By convention, the ovulation always occurs 14 days before the beginning of the next bleeding period. So for a cycle of 28 days we are talking about ovulation occurring in the 15th day while for a cycle of 32 days, ovulation occurs day 19.


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

2) Durnell K, Likis FE. (2011) Women's Gynecologic Health. Jones & Bartlett Publishers.

26 Dec, 2014