Menstrual calendar

What Is Menstrual Calendar?: How To Calculate The Onset Of Menstruation

The menstrual calendar is an important tool that allows you to know and monitor the status of your menstrual cycle .

During the period between one menstruation and the next, in fact, the woman’s reproductive system undergoes various structural and functional modifications, which recur every month . Such changes occur from puberty to menopause and are directly related to reproduction and fertility .
For these reasons, noting the beginning of the menstrual flow on the calendar or diary every month is a good habit to adopt in order to have a more precise idea of ​​the duration and regularity of one’s cycle and to recognize its alterations.
This tool is also useful to clearly identify the most fertile days , if you want to start or postpone a pregnancy .

What Is The Menstrual Cycle (In Brief)

The menstrual cycle is the time interval from the 1st day of a menstrual period to the day before the start of the next flow. During this period, a sequence of physiological events takes place, the purpose of which is the maturation of the egg cell ( female gamete ) and the preparation of an “environment” suitable for its eventual implantation. In other words, the processes of the menstrual cycle prepare the ground for a possible pregnancy, in the event that fertilization of the oocyte by a sperm of male origin occurs.


The menstrual calendar makes it possible to know the duration and regularity of the cycle and helps to identify variations with respect to the norm. Note the data relating to the frequency of menstruation in the diary should be a good habit for every woman, since the occurrence of the menarche , ie from the appearance of the first flow . This event marks the beginning of puberty and coincides with the entrance into childbearing age.
The menstrual calendar can provide useful information about women’s health : it helps manage the various aspects of the premenstrual syndrome , it helps to identify the fertile days when you want to have oravoid pregnancy etc.
For this reason, it is advisable to show the gynecologist your menstrual calendar, especially in the presence of any significant anomaly.

Duration, Frequency And Alterations Of The Menstrual Cycle

  • menstrual cycle is considered normal when it occurs at regular intervals of 28 days . However, a frequency of 25 to 36 days and a certain individual variability (the length of the cycle can change from month to month) should be considered normal. In any case, to be considered regular, between one period and the next there must not be a “gap” of more than 4 days (more or less).
  • Menstruation , i.e. the loss of blood that occurs each month, lasts an average of 3 to 7 days .
  • Any changes in the length of the menstrual cycle are most likely determined by the length of the period preceding ovulation ( follicular phase ). This first phase of the cycle, although having an average duration of about 14 days, can undergo fluctuations, which vary from 1 to 3 weeks. For most women, the luteal phase (period from ovulation to the start of menstruation) is more constant, taking 12 to 16 days (average duration: 14 days).
  • The phases of the menstrual cycle are associated with the periodic and regular secretion of ovarian, hypothalamic and pituitary hormones directly related to fertility. Therefore, various structures of the body ( central nervous system , hypothalamus , pituitary gland and ovaries ) contribute to maintaining the regularity of menstruation, ovulation and other related events .

What Happens During The Menstrual Cycle?

  • Menstruation – The beginning of each cycle is represented by the first day in which menstrual flow appears, i.e. a loss of blood mixed with tissue from the surface of the uterine wall ( endometrium ). This physiological phenomenon allows the uterus to shed the lining built up during the previous menstrual cycle. Typically, menstruation lasts 3-7 days.
  • Preparing for Ovulation – During the first part of the menstrual cycle, the pituitary initiates the secretion of follicle stimulating hormone (FSH), which stimulates the maturation of a “dominant” egg cell . At the same time, there is a progressive increase in the blood levels of estradiol (produced by the ovary). This determines a progressive thickening of the endometrium , which thus prepares itself to receive the mature egg cell in case it is fertilized.
  • Ovulation – Around the 14th day of the cycle, there is a sudden increase in luteinizing hormone (LH) which causes the ovarian follicle to rupture, with the expulsion of the mature egg inside the fallopian tube . During the 24 hours following this event, the egg cell is available for the eventual encounter with the sperm of male origin. The release of the oocyte is, therefore, a fundamental prerequisite for conception.
  • After Ovulation – What’s left of the “burst” follicle turns into the corpus luteum, which produces progesterone . The latter is a hormone necessary for the early stages of a possible pregnancy. If conception does not occur, there is a rapid fall in progesterone levels due to functional exhaustion of the corpus luteum; this triggers the phenomena that will lead to the flaking of the uterine wall and the subsequent menstruation. Otherwise, the fertilized egg nestles in the uterus, where it finds the most favorable environment for its implantation and the continuation of the pregnancy.

What Is It For

The menstrual cycle is an indicator of a woman’s health . For this reason, it is useful to understand how it works and keep it under control, month by month, with tools, such as the calendar, to recognize irregularities. Knowing how to calculate its progress is a way to get to know your body better and become aware of the periodic events that follow one another in the reproductive cycle.
The menstrual calendar allows you to predict on which day your period is expected , to prepare and not be caught by surprise.
The monthly recording of the beginning and end of the flow helps to understand if the organism reacts to stressor to other particular factors (e.g. seasonal climatic changes, reduced quality of sleep , etc.), which can influence the menstrual cycle, increasing or decreasing the duration of bleeding .
Collecting this data can also help women to:

  • Remember when they had sex ;
  • Planning the intake of the contraceptive pill ;
  • Avoid major gynecological problems (some pathologies of the female reproductive system involve the irregularity and variation of the frequency of the cycle among the initial symptoms ).

Finally, the menstrual calendar allows you to identify which days are the most fertile when trying to conceive a child or if you want to avoid pregnancy.

How Does It Work

How To Calculate The Onset Of Menstruation

To calculate the length of the cycle with the menstrual calendar, the period from the first day on which the flow appears (1st day of the cycle) to the day before the start of the next menstruation must be considered.
In the case of a regular 28 day cycle, ovulation (i.e. the moment when the ovary releases the egg cell) will occur 14 days before the next bleeding starts.

Fertile Days: What Are They?

In each menstrual cycle, the most favorable moment for conception coincides with ovulation and with the days around this event.
If the woman has regular cycles, this process occurs approximately every 28 days. After the onset of menstruation, an oocyte (as a rule, one for each menstrual cycle) takes an average of 14 days to mature and, under the hormonal stimulus , leave the follicle that contains it to enter the tube. From here, the egg cell begins its journey towards the uterus where it nests if, on its way, it is fertilized by a sperm.
Indicatively, the period in which it is possible for the egg to be fertilized begins 4-5 days before ovulation and ends 1-2 days after. This is possible in consideration of the fact that the egg cell matures when it is expelled from the ovary manages to survive about 24 hours, while the spermatozoa can remain viable in the female genital system up to 72-96 hours after intercourse.


In summary, the menstrual calendar is useful for the following reasons:

  • It allows you to predict on which day the onset of menstruation is expected;
  • It allows you to have a more precise idea of ​​the duration and regularity of your menstrual cycle, helping to recognize significant alterations (to be reported to the gynecologist);
  • Helps manage various aspects of PMS;
  • Identify your fertile days, should you wish to become pregnant or postpone a pregnancy.

What To Pay Attention To

There are many reasons why a period may be delayed and may include:

  • Pregnancy or breastfeeding ;
  • Period of strong emotions and stress;
  • Eating disorders (e.g. anorexia nervosa ), sudden weight loss or gain and excessive physical activity ;
  • polycystic ovarian syndrome (PCOS) ;
  • Premature ovarian failure;
  • Pelvic inflammatory disease (PID);
  • Uterine fibroids ;
  • Thyroid disorders ;
  • Stopping the birth control pill.

The greatest changes in cycle length occur in the early years following menarche and in premenopause . In case of alteration or interruption of the menstrual cycle (previously regular), to avoid confusing one of these causes, it is good to consult a doctor.

Main alterations of the menstrual cycle
Polymenorrhea Less than 25 day pace (short cycles, with closely spaced flows)
Oligomenorrhea Over 36-day pace (long cycles, with spaced flows)
Amenorrhea Absence of menstruation for at least 3 months
Menorrhagia Excessively abundant menstrual bleeding, of a haemorrhagic nature, and/or of a longer than normal duration
Menometrorrhagia Abundant menstruation that continues even in the intermenstrual period
Metrorrhagia Blood loss that occurs independently of menstrual bleeding or at a time when there should be no menstruation (pregnancy, menopause, or before puberty); if the intermenstrual blood loss is small, however, we speak of spotting
Hypomenorrhea Menstrual blood loss less than 20 mL (less than normal menstrual flow)
Hypermenorrhea Menstrual blood loss greater than 80 ml ( heavy menstrual flow )

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